diff --git a/clientapi/routing/account_data.go b/clientapi/routing/account_data.go
index 7eacf9cc9..a6477fdea 100644
--- a/clientapi/routing/account_data.go
+++ b/clientapi/routing/account_data.go
@@ -145,8 +145,23 @@ func SaveReadMarker(
 	userAPI api.ClientUserAPI, rsAPI roomserverAPI.ClientRoomserverAPI,
 	syncProducer *producers.SyncAPIProducer, device *api.Device, roomID string,
 ) util.JSONResponse {
+	fullUserID, err := spec.NewUserID(device.UserID, true)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusForbidden,
+			JSON: spec.Forbidden("userID doesn't have power level to change visibility"),
+		}
+	}
+	senderID, err := rsAPI.QuerySenderIDForUser(req.Context(), roomID, *fullUserID)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusForbidden,
+			JSON: spec.Forbidden("userID doesn't have power level to change visibility"),
+		}
+	}
+
 	// Verify that the user is a member of this room
-	resErr := checkMemberInRoom(req.Context(), rsAPI, device.UserID, roomID)
+	resErr := checkMemberInRoom(req.Context(), rsAPI, senderID, roomID)
 	if resErr != nil {
 		return *resErr
 	}
diff --git a/clientapi/routing/aliases.go b/clientapi/routing/aliases.go
index f6603be8b..dfc8325de 100644
--- a/clientapi/routing/aliases.go
+++ b/clientapi/routing/aliases.go
@@ -55,9 +55,23 @@ func GetAliases(
 		visibility = content.HistoryVisibility
 	}
 	if visibility != spec.WorldReadable {
+		fullUserID, err := spec.NewUserID(device.UserID, true)
+		if err != nil {
+			return util.JSONResponse{
+				Code: http.StatusForbidden,
+				JSON: spec.Forbidden("userID doesn't have power level to change visibility"),
+			}
+		}
+		senderID, err := rsAPI.QuerySenderIDForUser(req.Context(), roomID, *fullUserID)
+		if err != nil {
+			return util.JSONResponse{
+				Code: http.StatusForbidden,
+				JSON: spec.Forbidden("userID doesn't have power level to change visibility"),
+			}
+		}
 		queryReq := api.QueryMembershipForUserRequest{
-			RoomID: roomID,
-			UserID: device.UserID,
+			RoomID:   roomID,
+			SenderID: senderID,
 		}
 		var queryRes api.QueryMembershipForUserResponse
 		if err := rsAPI.QueryMembershipForUser(req.Context(), &queryReq, &queryRes); err != nil {
diff --git a/clientapi/routing/directory.go b/clientapi/routing/directory.go
index 034296f45..516a158e1 100644
--- a/clientapi/routing/directory.go
+++ b/clientapi/routing/directory.go
@@ -314,30 +314,6 @@ func SetVisibility(
 	req *http.Request, rsAPI roomserverAPI.ClientRoomserverAPI, dev *userapi.Device,
 	roomID string,
 ) util.JSONResponse {
-	resErr := checkMemberInRoom(req.Context(), rsAPI, dev.UserID, roomID)
-	if resErr != nil {
-		return *resErr
-	}
-
-	queryEventsReq := roomserverAPI.QueryLatestEventsAndStateRequest{
-		RoomID: roomID,
-		StateToFetch: []gomatrixserverlib.StateKeyTuple{{
-			EventType: spec.MRoomPowerLevels,
-			StateKey:  "",
-		}},
-	}
-	var queryEventsRes roomserverAPI.QueryLatestEventsAndStateResponse
-	err := rsAPI.QueryLatestEventsAndState(req.Context(), &queryEventsReq, &queryEventsRes)
-	if err != nil || len(queryEventsRes.StateEvents) == 0 {
-		util.GetLogger(req.Context()).WithError(err).Error("could not query events from room")
-		return util.JSONResponse{
-			Code: http.StatusInternalServerError,
-			JSON: spec.InternalServerError{},
-		}
-	}
-
-	// NOTSPEC: Check if the user's power is greater than power required to change m.room.canonical_alias event
-	power, _ := gomatrixserverlib.NewPowerLevelContentFromEvent(queryEventsRes.StateEvents[0].PDU)
 	fullUserID, err := spec.NewUserID(dev.UserID, true)
 	if err != nil {
 		return util.JSONResponse{
@@ -352,6 +328,31 @@ func SetVisibility(
 			JSON: spec.Forbidden("userID doesn't have power level to change visibility"),
 		}
 	}
+
+	resErr := checkMemberInRoom(req.Context(), rsAPI, senderID, roomID)
+	if resErr != nil {
+		return *resErr
+	}
+
+	queryEventsReq := roomserverAPI.QueryLatestEventsAndStateRequest{
+		RoomID: roomID,
+		StateToFetch: []gomatrixserverlib.StateKeyTuple{{
+			EventType: spec.MRoomPowerLevels,
+			StateKey:  "",
+		}},
+	}
+	var queryEventsRes roomserverAPI.QueryLatestEventsAndStateResponse
+	err = rsAPI.QueryLatestEventsAndState(req.Context(), &queryEventsReq, &queryEventsRes)
+	if err != nil || len(queryEventsRes.StateEvents) == 0 {
+		util.GetLogger(req.Context()).WithError(err).Error("could not query events from room")
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
+	}
+
+	// NOTSPEC: Check if the user's power is greater than power required to change m.room.canonical_alias event
+	power, _ := gomatrixserverlib.NewPowerLevelContentFromEvent(queryEventsRes.StateEvents[0].PDU)
 	if power.UserLevel(senderID) < power.EventLevel(spec.MRoomCanonicalAlias, true) {
 		return util.JSONResponse{
 			Code: http.StatusForbidden,
diff --git a/clientapi/routing/leaveroom.go b/clientapi/routing/leaveroom.go
index fbf148264..6d215c826 100644
--- a/clientapi/routing/leaveroom.go
+++ b/clientapi/routing/leaveroom.go
@@ -29,10 +29,25 @@ func LeaveRoomByID(
 	rsAPI roomserverAPI.ClientRoomserverAPI,
 	roomID string,
 ) util.JSONResponse {
+	userID, err := spec.NewUserID(device.UserID, true)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: spec.Unknown("device userID is invalid"),
+		}
+	}
+	senderID, err := rsAPI.QuerySenderIDForUser(req.Context(), roomID, *userID)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: spec.Unknown("could not find senderID for this user"),
+		}
+	}
+
 	// Prepare to ask the roomserver to perform the room join.
 	leaveReq := roomserverAPI.PerformLeaveRequest{
 		RoomID: roomID,
-		UserID: device.UserID,
+		Leaver: roomserverAPI.SenderUserIDPair{SenderID: senderID, UserID: *userID},
 	}
 	leaveRes := roomserverAPI.PerformLeaveResponse{}
 
diff --git a/clientapi/routing/membership.go b/clientapi/routing/membership.go
index d5e1ce1f6..e23abf147 100644
--- a/clientapi/routing/membership.go
+++ b/clientapi/routing/membership.go
@@ -57,15 +57,6 @@ func SendBan(
 		}
 	}
 
-	errRes := checkMemberInRoom(req.Context(), rsAPI, device.UserID, roomID)
-	if errRes != nil {
-		return *errRes
-	}
-
-	pl, errRes := getPowerlevels(req, rsAPI, roomID)
-	if errRes != nil {
-		return *errRes
-	}
 	fullUserID, err := spec.NewUserID(device.UserID, true)
 	if err != nil {
 		return util.JSONResponse{
@@ -80,6 +71,16 @@ func SendBan(
 			JSON: spec.Forbidden("You don't have permission to ban this user, unknown senderID"),
 		}
 	}
+
+	errRes := checkMemberInRoom(req.Context(), rsAPI, senderID, roomID)
+	if errRes != nil {
+		return *errRes
+	}
+
+	pl, errRes := getPowerlevels(req, rsAPI, roomID)
+	if errRes != nil {
+		return *errRes
+	}
 	allowedToBan := pl.UserLevel(senderID) >= pl.Ban
 	if !allowedToBan {
 		return util.JSONResponse{
@@ -147,15 +148,6 @@ func SendKick(
 		}
 	}
 
-	errRes := checkMemberInRoom(req.Context(), rsAPI, device.UserID, roomID)
-	if errRes != nil {
-		return *errRes
-	}
-
-	pl, errRes := getPowerlevels(req, rsAPI, roomID)
-	if errRes != nil {
-		return *errRes
-	}
 	fullUserID, err := spec.NewUserID(device.UserID, true)
 	if err != nil {
 		return util.JSONResponse{
@@ -170,6 +162,16 @@ func SendKick(
 			JSON: spec.Forbidden("You don't have permission to kick this user, unknown senderID"),
 		}
 	}
+
+	errRes := checkMemberInRoom(req.Context(), rsAPI, senderID, roomID)
+	if errRes != nil {
+		return *errRes
+	}
+
+	pl, errRes := getPowerlevels(req, rsAPI, roomID)
+	if errRes != nil {
+		return *errRes
+	}
 	allowedToKick := pl.UserLevel(senderID) >= pl.Kick
 	if !allowedToKick {
 		return util.JSONResponse{
@@ -178,10 +180,24 @@ func SendKick(
 		}
 	}
 
+	bodyUserID, err := spec.NewUserID(body.UserID, true)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: spec.BadJSON("body userID is invalid"),
+		}
+	}
+	bodySenderID, err := rsAPI.QuerySenderIDForUser(req.Context(), roomID, *bodyUserID)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: spec.NotFound("body userID has no matching senderID"),
+		}
+	}
 	var queryRes roomserverAPI.QueryMembershipForUserResponse
 	err = rsAPI.QueryMembershipForUser(req.Context(), &roomserverAPI.QueryMembershipForUserRequest{
-		RoomID: roomID,
-		UserID: body.UserID,
+		RoomID:   roomID,
+		SenderID: bodySenderID,
 	}, &queryRes)
 	if err != nil {
 		return util.ErrorResponse(err)
@@ -213,15 +229,44 @@ func SendUnban(
 		}
 	}
 
-	errRes := checkMemberInRoom(req.Context(), rsAPI, device.UserID, roomID)
+	fullUserID, err := spec.NewUserID(device.UserID, true)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusForbidden,
+			JSON: spec.Forbidden("You don't have permission to kick this user, bad userID"),
+		}
+	}
+	senderID, err := rsAPI.QuerySenderIDForUser(req.Context(), roomID, *fullUserID)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusForbidden,
+			JSON: spec.Forbidden("You don't have permission to kick this user, unknown senderID"),
+		}
+	}
+
+	errRes := checkMemberInRoom(req.Context(), rsAPI, senderID, roomID)
 	if errRes != nil {
 		return *errRes
 	}
 
+	bodyUserID, err := spec.NewUserID(body.UserID, true)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: spec.BadJSON("body userID is invalid"),
+		}
+	}
+	bodySenderID, err := rsAPI.QuerySenderIDForUser(req.Context(), roomID, *bodyUserID)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: spec.NotFound("body userID has no matching senderID"),
+		}
+	}
 	var queryRes roomserverAPI.QueryMembershipForUserResponse
-	err := rsAPI.QueryMembershipForUser(req.Context(), &roomserverAPI.QueryMembershipForUserRequest{
-		RoomID: roomID,
-		UserID: body.UserID,
+	err = rsAPI.QueryMembershipForUser(req.Context(), &roomserverAPI.QueryMembershipForUserRequest{
+		RoomID:   roomID,
+		SenderID: bodySenderID,
 	}, &queryRes)
 	if err != nil {
 		return util.ErrorResponse(err)
@@ -272,7 +317,22 @@ func SendInvite(
 		}
 	}
 
-	errRes := checkMemberInRoom(req.Context(), rsAPI, device.UserID, roomID)
+	fullUserID, err := spec.NewUserID(device.UserID, true)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusForbidden,
+			JSON: spec.Forbidden("You don't have permission to kick this user, bad userID"),
+		}
+	}
+	senderID, err := rsAPI.QuerySenderIDForUser(req.Context(), roomID, *fullUserID)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusForbidden,
+			JSON: spec.Forbidden("You don't have permission to kick this user, unknown senderID"),
+		}
+	}
+
+	errRes := checkMemberInRoom(req.Context(), rsAPI, senderID, roomID)
 	if errRes != nil {
 		return *errRes
 	}
@@ -508,11 +568,11 @@ func checkAndProcessThreepid(
 	return
 }
 
-func checkMemberInRoom(ctx context.Context, rsAPI roomserverAPI.ClientRoomserverAPI, userID, roomID string) *util.JSONResponse {
+func checkMemberInRoom(ctx context.Context, rsAPI roomserverAPI.ClientRoomserverAPI, senderID spec.SenderID, roomID string) *util.JSONResponse {
 	var membershipRes roomserverAPI.QueryMembershipForUserResponse
 	err := rsAPI.QueryMembershipForUser(ctx, &roomserverAPI.QueryMembershipForUserRequest{
-		RoomID: roomID,
-		UserID: userID,
+		RoomID:   roomID,
+		SenderID: senderID,
 	}, &membershipRes)
 	if err != nil {
 		util.GetLogger(ctx).WithError(err).Error("QueryMembershipForUser: could not query membership for user")
@@ -536,12 +596,28 @@ func SendForget(
 ) util.JSONResponse {
 	ctx := req.Context()
 	logger := util.GetLogger(ctx).WithField("roomID", roomID).WithField("userID", device.UserID)
+
+	fullUserID, err := spec.NewUserID(device.UserID, true)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusForbidden,
+			JSON: spec.Forbidden("You don't have permission to kick this user, bad userID"),
+		}
+	}
+	senderID, err := rsAPI.QuerySenderIDForUser(req.Context(), roomID, *fullUserID)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusForbidden,
+			JSON: spec.Forbidden("You don't have permission to kick this user, unknown senderID"),
+		}
+	}
+
 	var membershipRes roomserverAPI.QueryMembershipForUserResponse
 	membershipReq := roomserverAPI.QueryMembershipForUserRequest{
-		RoomID: roomID,
-		UserID: device.UserID,
+		RoomID:   roomID,
+		SenderID: senderID,
 	}
-	err := rsAPI.QueryMembershipForUser(ctx, &membershipReq, &membershipRes)
+	err = rsAPI.QueryMembershipForUser(ctx, &membershipReq, &membershipRes)
 	if err != nil {
 		logger.WithError(err).Error("QueryMembershipForUser: could not query membership for user")
 		return util.JSONResponse{
diff --git a/clientapi/routing/redaction.go b/clientapi/routing/redaction.go
index 22474fc08..4d7f9a27a 100644
--- a/clientapi/routing/redaction.go
+++ b/clientapi/routing/redaction.go
@@ -47,7 +47,22 @@ func SendRedaction(
 	txnID *string,
 	txnCache *transactions.Cache,
 ) util.JSONResponse {
-	resErr := checkMemberInRoom(req.Context(), rsAPI, device.UserID, roomID)
+	fullUserID, userIDErr := spec.NewUserID(device.UserID, true)
+	if userIDErr != nil {
+		return util.JSONResponse{
+			Code: http.StatusForbidden,
+			JSON: spec.Forbidden("userID doesn't have power level to redact"),
+		}
+	}
+	senderID, queryErr := rsAPI.QuerySenderIDForUser(req.Context(), roomID, *fullUserID)
+	if queryErr != nil {
+		return util.JSONResponse{
+			Code: http.StatusForbidden,
+			JSON: spec.Forbidden("userID doesn't have power level to redact"),
+		}
+	}
+
+	resErr := checkMemberInRoom(req.Context(), rsAPI, senderID, roomID)
 	if resErr != nil {
 		return *resErr
 	}
@@ -73,21 +88,6 @@ func SendRedaction(
 		}
 	}
 
-	fullUserID, userIDErr := spec.NewUserID(device.UserID, true)
-	if userIDErr != nil {
-		return util.JSONResponse{
-			Code: http.StatusForbidden,
-			JSON: spec.Forbidden("userID doesn't have power level to redact"),
-		}
-	}
-	senderID, queryErr := rsAPI.QuerySenderIDForUser(req.Context(), roomID, *fullUserID)
-	if queryErr != nil {
-		return util.JSONResponse{
-			Code: http.StatusForbidden,
-			JSON: spec.Forbidden("userID doesn't have power level to redact"),
-		}
-	}
-
 	// "Users may redact their own events, and any user with a power level greater than or equal
 	// to the redact power level of the room may redact events there"
 	// https://matrix.org/docs/spec/client_server/r0.6.1#put-matrix-client-r0-rooms-roomid-redact-eventid-txnid
diff --git a/clientapi/routing/sendtyping.go b/clientapi/routing/sendtyping.go
index c5b29297a..a43fd162e 100644
--- a/clientapi/routing/sendtyping.go
+++ b/clientapi/routing/sendtyping.go
@@ -43,8 +43,23 @@ func SendTyping(
 		}
 	}
 
+	fullUserID, err := spec.NewUserID(userID, true)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusForbidden,
+			JSON: spec.Forbidden("userID doesn't have power level to change visibility"),
+		}
+	}
+	senderID, err := rsAPI.QuerySenderIDForUser(req.Context(), roomID, *fullUserID)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusForbidden,
+			JSON: spec.Forbidden("userID doesn't have power level to change visibility"),
+		}
+	}
+
 	// Verify that the user is a member of this room
-	resErr := checkMemberInRoom(req.Context(), rsAPI, userID, roomID)
+	resErr := checkMemberInRoom(req.Context(), rsAPI, senderID, roomID)
 	if resErr != nil {
 		return *resErr
 	}
diff --git a/clientapi/routing/server_notices.go b/clientapi/routing/server_notices.go
index 06714ed1f..b1f2e63f1 100644
--- a/clientapi/routing/server_notices.go
+++ b/clientapi/routing/server_notices.go
@@ -52,6 +52,7 @@ type sendServerNoticeRequest struct {
 	StateKey string `json:"state_key,omitempty"`
 }
 
+// nolint:gocyclo
 // SendServerNotice sends a message to a specific user. It can only be invoked by an admin.
 func SendServerNotice(
 	req *http.Request,
@@ -187,9 +188,24 @@ func SendServerNotice(
 		}
 	} else {
 		// we've found a room in common, check the membership
+		fullUserID, err := spec.NewUserID(r.UserID, true)
+		if err != nil {
+			return util.JSONResponse{
+				Code: http.StatusForbidden,
+				JSON: spec.Forbidden("userID doesn't have power level to change visibility"),
+			}
+		}
+		senderID, err := rsAPI.QuerySenderIDForUser(req.Context(), roomID, *fullUserID)
+		if err != nil {
+			return util.JSONResponse{
+				Code: http.StatusForbidden,
+				JSON: spec.Forbidden("userID doesn't have power level to change visibility"),
+			}
+		}
+
 		roomID = commonRooms[0]
 		membershipRes := api.QueryMembershipForUserResponse{}
-		err := rsAPI.QueryMembershipForUser(ctx, &api.QueryMembershipForUserRequest{UserID: r.UserID, RoomID: roomID}, &membershipRes)
+		err = rsAPI.QueryMembershipForUser(ctx, &api.QueryMembershipForUserRequest{SenderID: senderID, RoomID: roomID}, &membershipRes)
 		if err != nil {
 			util.GetLogger(ctx).WithError(err).Error("unable to query membership for user")
 			return util.JSONResponse{
@@ -234,7 +250,7 @@ func SendServerNotice(
 		ctx, rsAPI,
 		api.KindNew,
 		[]*types.HeaderedEvent{
-			&types.HeaderedEvent{PDU: e},
+			{PDU: e},
 		},
 		device.UserDomain(),
 		cfgClient.Matrix.ServerName,
diff --git a/clientapi/routing/state.go b/clientapi/routing/state.go
index d74002928..8eea2f308 100644
--- a/clientapi/routing/state.go
+++ b/clientapi/routing/state.go
@@ -99,9 +99,25 @@ func OnIncomingStateRequest(ctx context.Context, device *userapi.Device, rsAPI a
 	if !worldReadable {
 		// The room isn't world-readable so try to work out based on the
 		// user's membership if we want the latest state or not.
-		err := rsAPI.QueryMembershipForUser(ctx, &api.QueryMembershipForUserRequest{
-			RoomID: roomID,
-			UserID: device.UserID,
+		userID, err := spec.NewUserID(device.UserID, true)
+		if err != nil {
+			util.GetLogger(ctx).WithError(err).Error("UserID is invalid")
+			return util.JSONResponse{
+				Code: http.StatusBadRequest,
+				JSON: spec.Unknown("Device UserID is invalid"),
+			}
+		}
+		senderID, err := rsAPI.QuerySenderIDForUser(ctx, roomID, *userID)
+		if err != nil {
+			util.GetLogger(ctx).WithError(err).Error("No matching senderID for this device")
+			return util.JSONResponse{
+				Code: http.StatusNotFound,
+				JSON: spec.NotFound("Unable to find senderID for user"),
+			}
+		}
+		err = rsAPI.QueryMembershipForUser(ctx, &api.QueryMembershipForUserRequest{
+			RoomID:   roomID,
+			SenderID: senderID,
 		}, &membershipRes)
 		if err != nil {
 			util.GetLogger(ctx).WithError(err).Error("Failed to QueryMembershipForUser")
@@ -265,11 +281,27 @@ func OnIncomingStateTypeRequest(
 	// membershipRes will only be populated if the room is not world-readable.
 	var membershipRes api.QueryMembershipForUserResponse
 	if !worldReadable {
+		userID, err := spec.NewUserID(device.UserID, true)
+		if err != nil {
+			util.GetLogger(ctx).WithError(err).Error("UserID is invalid")
+			return util.JSONResponse{
+				Code: http.StatusBadRequest,
+				JSON: spec.Unknown("Device UserID is invalid"),
+			}
+		}
+		senderID, err := rsAPI.QuerySenderIDForUser(ctx, roomID, *userID)
+		if err != nil {
+			util.GetLogger(ctx).WithError(err).Error("No matching senderID for this device")
+			return util.JSONResponse{
+				Code: http.StatusNotFound,
+				JSON: spec.NotFound("Unable to find senderID for user"),
+			}
+		}
 		// The room isn't world-readable so try to work out based on the
 		// user's membership if we want the latest state or not.
-		err := rsAPI.QueryMembershipForUser(ctx, &api.QueryMembershipForUserRequest{
-			RoomID: roomID,
-			UserID: device.UserID,
+		err = rsAPI.QueryMembershipForUser(ctx, &api.QueryMembershipForUserRequest{
+			RoomID:   roomID,
+			SenderID: senderID,
 		}, &membershipRes)
 		if err != nil {
 			util.GetLogger(ctx).WithError(err).Error("Failed to QueryMembershipForUser")
diff --git a/go.mod b/go.mod
index 23da31ec1..af75040fe 100644
--- a/go.mod
+++ b/go.mod
@@ -22,7 +22,7 @@ require (
 	github.com/matrix-org/dugong v0.0.0-20210921133753-66e6b1c67e2e
 	github.com/matrix-org/go-sqlite3-js v0.0.0-20220419092513-28aa791a1c91
 	github.com/matrix-org/gomatrix v0.0.0-20220926102614-ceba4d9f7530
-	github.com/matrix-org/gomatrixserverlib v0.0.0-20230607195007-f30c42b17b85
+	github.com/matrix-org/gomatrixserverlib v0.0.0-20230608195455-508c2cae4483
 	github.com/matrix-org/pinecone v0.11.1-0.20230210171230-8c3b24f2649a
 	github.com/matrix-org/util v0.0.0-20221111132719-399730281e66
 	github.com/mattn/go-sqlite3 v1.14.16
diff --git a/go.sum b/go.sum
index 2e8d258e5..c99d9a07a 100644
--- a/go.sum
+++ b/go.sum
@@ -323,8 +323,8 @@ github.com/matrix-org/go-sqlite3-js v0.0.0-20220419092513-28aa791a1c91 h1:s7fexw
 github.com/matrix-org/go-sqlite3-js v0.0.0-20220419092513-28aa791a1c91/go.mod h1:e+cg2q7C7yE5QnAXgzo512tgFh1RbQLC0+jozuegKgo=
 github.com/matrix-org/gomatrix v0.0.0-20220926102614-ceba4d9f7530 h1:kHKxCOLcHH8r4Fzarl4+Y3K5hjothkVW5z7T1dUM11U=
 github.com/matrix-org/gomatrix v0.0.0-20220926102614-ceba4d9f7530/go.mod h1:/gBX06Kw0exX1HrwmoBibFA98yBk/jxKpGVeyQbff+s=
-github.com/matrix-org/gomatrixserverlib v0.0.0-20230607195007-f30c42b17b85 h1:WkmHgdQvpPBxGo/huuCQVR9FWmdkKOcAuQHZBmcHK3g=
-github.com/matrix-org/gomatrixserverlib v0.0.0-20230607195007-f30c42b17b85/go.mod h1:H9V9N3Uqn1bBJqYJNGK1noqtgJTaCEhtTdcH/mp50uU=
+github.com/matrix-org/gomatrixserverlib v0.0.0-20230608195455-508c2cae4483 h1:T7y2bnp0l0JVGqegAmpOdkaENFiA7raSNSdYz0PXxaI=
+github.com/matrix-org/gomatrixserverlib v0.0.0-20230608195455-508c2cae4483/go.mod h1:H9V9N3Uqn1bBJqYJNGK1noqtgJTaCEhtTdcH/mp50uU=
 github.com/matrix-org/pinecone v0.11.1-0.20230210171230-8c3b24f2649a h1:awrPDf9LEFySxTLKYBMCiObelNx/cBuv/wzllvCCH3A=
 github.com/matrix-org/pinecone v0.11.1-0.20230210171230-8c3b24f2649a/go.mod h1:HchJX9oKMXaT2xYFs0Ha/6Zs06mxLU8k6F1ODnrGkeQ=
 github.com/matrix-org/util v0.0.0-20221111132719-399730281e66 h1:6z4KxomXSIGWqhHcfzExgkH3Z3UkIXry4ibJS4Aqz2Y=
diff --git a/roomserver/api/api.go b/roomserver/api/api.go
index 8c2cbd6b2..53b77e4c7 100644
--- a/roomserver/api/api.go
+++ b/roomserver/api/api.go
@@ -34,11 +34,11 @@ func (e ErrNotAllowed) Error() string {
 
 type RestrictedJoinAPI interface {
 	CurrentStateEvent(ctx context.Context, roomID spec.RoomID, eventType string, stateKey string) (gomatrixserverlib.PDU, error)
-	InvitePending(ctx context.Context, roomID spec.RoomID, userID spec.UserID) (bool, error)
-	RestrictedRoomJoinInfo(ctx context.Context, roomID spec.RoomID, userID spec.UserID, localServerName spec.ServerName) (*gomatrixserverlib.RestrictedRoomJoinInfo, error)
+	InvitePending(ctx context.Context, roomID spec.RoomID, senderID spec.SenderID) (bool, error)
+	RestrictedRoomJoinInfo(ctx context.Context, roomID spec.RoomID, senderID spec.SenderID, localServerName spec.ServerName) (*gomatrixserverlib.RestrictedRoomJoinInfo, error)
 	QueryRoomInfo(ctx context.Context, roomID spec.RoomID) (*types.RoomInfo, error)
 	QueryServerJoinedToRoom(ctx context.Context, req *QueryServerJoinedToRoomRequest, res *QueryServerJoinedToRoomResponse) error
-	UserJoinedToRoom(ctx context.Context, roomID types.RoomNID, userID spec.UserID) (bool, error)
+	UserJoinedToRoom(ctx context.Context, roomID types.RoomNID, senderID spec.SenderID) (bool, error)
 	LocallyJoinedUsers(ctx context.Context, roomVersion gomatrixserverlib.RoomVersion, roomNID types.RoomNID) ([]gomatrixserverlib.PDU, error)
 }
 
@@ -238,15 +238,13 @@ type FederationRoomserverAPI interface {
 	// Takes lists of PrevEventIDs and AuthEventsIDs and uses them to calculate
 	// the state and auth chain to return.
 	QueryStateAndAuthChain(ctx context.Context, req *QueryStateAndAuthChainRequest, res *QueryStateAndAuthChainResponse) error
-	// Query if we think we're still in a room.
-	QueryServerJoinedToRoom(ctx context.Context, req *QueryServerJoinedToRoomRequest, res *QueryServerJoinedToRoomResponse) error
 	QueryPublishedRooms(ctx context.Context, req *QueryPublishedRoomsRequest, res *QueryPublishedRoomsResponse) error
 	// Query missing events for a room from roomserver
 	QueryMissingEvents(ctx context.Context, req *QueryMissingEventsRequest, res *QueryMissingEventsResponse) error
 	// Query whether a server is allowed to see an event
 	QueryServerAllowedToSeeEvent(ctx context.Context, serverName spec.ServerName, eventID string) (allowed bool, err error)
 	QueryRoomsForUser(ctx context.Context, req *QueryRoomsForUserRequest, res *QueryRoomsForUserResponse) error
-	QueryRestrictedJoinAllowed(ctx context.Context, roomID spec.RoomID, userID spec.UserID) (string, error)
+	QueryRestrictedJoinAllowed(ctx context.Context, roomID spec.RoomID, senderID spec.SenderID) (string, error)
 	PerformInboundPeek(ctx context.Context, req *PerformInboundPeekRequest, res *PerformInboundPeekResponse) error
 	HandleInvite(ctx context.Context, event *types.HeaderedEvent) error
 
@@ -254,12 +252,6 @@ type FederationRoomserverAPI interface {
 	// Query a given amount (or less) of events prior to a given set of events.
 	PerformBackfill(ctx context.Context, req *PerformBackfillRequest, res *PerformBackfillResponse) error
 
-	CurrentStateEvent(ctx context.Context, roomID spec.RoomID, eventType string, stateKey string) (gomatrixserverlib.PDU, error)
-	InvitePending(ctx context.Context, roomID spec.RoomID, userID spec.UserID) (bool, error)
-	QueryRoomInfo(ctx context.Context, roomID spec.RoomID) (*types.RoomInfo, error)
-	UserJoinedToRoom(ctx context.Context, roomID types.RoomNID, userID spec.UserID) (bool, error)
-	LocallyJoinedUsers(ctx context.Context, roomVersion gomatrixserverlib.RoomVersion, roomNID types.RoomNID) ([]gomatrixserverlib.PDU, error)
-
 	IsKnownRoom(ctx context.Context, roomID spec.RoomID) (bool, error)
 	StateQuerier() gomatrixserverlib.StateQuerier
 }
diff --git a/roomserver/api/output.go b/roomserver/api/output.go
index 16b504957..852b64206 100644
--- a/roomserver/api/output.go
+++ b/roomserver/api/output.go
@@ -215,8 +215,10 @@ type OutputNewInviteEvent struct {
 type OutputRetireInviteEvent struct {
 	// The ID of the "m.room.member" invite event.
 	EventID string
-	// The target user ID of the "m.room.member" invite event that was retired.
-	TargetUserID string
+	// The room ID of the "m.room.member" invite event.
+	RoomID string
+	// The target sender ID of the "m.room.member" invite event that was retired.
+	TargetSenderID spec.SenderID
 	// Optional event ID of the event that replaced the invite.
 	// This can be empty if the invite was rejected locally and we were unable
 	// to reach the server that originally sent the invite.
diff --git a/roomserver/api/perform.go b/roomserver/api/perform.go
index 6cbaf5b19..af775e350 100644
--- a/roomserver/api/perform.go
+++ b/roomserver/api/perform.go
@@ -11,6 +11,11 @@ import (
 	"github.com/matrix-org/util"
 )
 
+type SenderUserIDPair struct {
+	SenderID spec.SenderID
+	UserID   spec.UserID
+}
+
 type PerformCreateRoomRequest struct {
 	InvitedUsers              []string
 	RoomName                  string
@@ -41,8 +46,8 @@ type PerformJoinRequest struct {
 }
 
 type PerformLeaveRequest struct {
-	RoomID string `json:"room_id"`
-	UserID string `json:"user_id"`
+	RoomID string
+	Leaver SenderUserIDPair
 }
 
 type PerformLeaveResponse struct {
diff --git a/roomserver/api/query.go b/roomserver/api/query.go
index d79dcebbb..891797557 100644
--- a/roomserver/api/query.go
+++ b/roomserver/api/query.go
@@ -115,7 +115,7 @@ type QueryMembershipForUserRequest struct {
 	// ID of the room to fetch membership from
 	RoomID string `json:"room_id"`
 	// ID of the user for whom membership is requested
-	UserID string `json:"user_id"`
+	SenderID spec.SenderID `json:"user_id"`
 }
 
 // QueryMembershipForUserResponse is a response to QueryMembership
@@ -145,7 +145,7 @@ type QueryMembershipsForRoomRequest struct {
 	// Optional - ID of the user sending the request, for checking if the
 	// user is allowed to see the memberships. If not specified then all
 	// room memberships will be returned.
-	Sender string `json:"sender"`
+	SenderID spec.SenderID `json:"sender"`
 }
 
 // QueryMembershipsForRoomResponse is a response to QueryMembershipsForRoom
@@ -448,11 +448,11 @@ func (rq *JoinRoomQuerier) CurrentStateEvent(ctx context.Context, roomID spec.Ro
 	return rq.Roomserver.CurrentStateEvent(ctx, roomID, eventType, stateKey)
 }
 
-func (rq *JoinRoomQuerier) InvitePending(ctx context.Context, roomID spec.RoomID, userID spec.UserID) (bool, error) {
-	return rq.Roomserver.InvitePending(ctx, roomID, userID)
+func (rq *JoinRoomQuerier) InvitePending(ctx context.Context, roomID spec.RoomID, senderID spec.SenderID) (bool, error) {
+	return rq.Roomserver.InvitePending(ctx, roomID, senderID)
 }
 
-func (rq *JoinRoomQuerier) RestrictedRoomJoinInfo(ctx context.Context, roomID spec.RoomID, userID spec.UserID, localServerName spec.ServerName) (*gomatrixserverlib.RestrictedRoomJoinInfo, error) {
+func (rq *JoinRoomQuerier) RestrictedRoomJoinInfo(ctx context.Context, roomID spec.RoomID, senderID spec.SenderID, localServerName spec.ServerName) (*gomatrixserverlib.RestrictedRoomJoinInfo, error) {
 	roomInfo, err := rq.Roomserver.QueryRoomInfo(ctx, roomID)
 	if err != nil || roomInfo == nil || roomInfo.IsStub() {
 		return nil, err
@@ -468,7 +468,7 @@ func (rq *JoinRoomQuerier) RestrictedRoomJoinInfo(ctx context.Context, roomID sp
 		return nil, fmt.Errorf("InternalServerError: Failed to query room: %w", err)
 	}
 
-	userJoinedToRoom, err := rq.Roomserver.UserJoinedToRoom(ctx, types.RoomNID(roomInfo.RoomNID), userID)
+	userJoinedToRoom, err := rq.Roomserver.UserJoinedToRoom(ctx, types.RoomNID(roomInfo.RoomNID), senderID)
 	if err != nil {
 		util.GetLogger(ctx).WithError(err).Error("rsAPI.UserJoinedToRoom failed")
 		return nil, fmt.Errorf("InternalServerError: %w", err)
@@ -493,8 +493,8 @@ type MembershipQuerier struct {
 
 func (mq *MembershipQuerier) CurrentMembership(ctx context.Context, roomID spec.RoomID, senderID spec.SenderID) (string, error) {
 	req := QueryMembershipForUserRequest{
-		RoomID: roomID.String(),
-		UserID: string(senderID),
+		RoomID:   roomID.String(),
+		SenderID: senderID,
 	}
 	res := QueryMembershipForUserResponse{}
 	err := mq.Roomserver.QueryMembershipForUser(ctx, &req, &res)
diff --git a/roomserver/internal/helpers/helpers.go b/roomserver/internal/helpers/helpers.go
index 95397cd5e..eee8e1a55 100644
--- a/roomserver/internal/helpers/helpers.go
+++ b/roomserver/internal/helpers/helpers.go
@@ -55,9 +55,10 @@ func UpdateToInviteMembership(
 			Type: api.OutputTypeRetireInviteEvent,
 			RetireInviteEvent: &api.OutputRetireInviteEvent{
 				EventID:          eventID,
+				RoomID:           add.RoomID(),
 				Membership:       spec.Join,
 				RetiredByEventID: add.EventID(),
-				TargetUserID:     *add.StateKey(),
+				TargetSenderID:   spec.SenderID(*add.StateKey()),
 			},
 		})
 	}
@@ -99,8 +100,8 @@ func IsServerCurrentlyInRoom(ctx context.Context, db storage.Database, serverNam
 
 func IsInvitePending(
 	ctx context.Context, db storage.Database,
-	roomID, userID string,
-) (bool, string, string, gomatrixserverlib.PDU, error) {
+	roomID string, senderID spec.SenderID,
+) (bool, spec.SenderID, string, gomatrixserverlib.PDU, error) {
 	// Look up the room NID for the supplied room ID.
 	info, err := db.RoomInfo(ctx, roomID)
 	if err != nil {
@@ -111,13 +112,13 @@ func IsInvitePending(
 	}
 
 	// Look up the state key NID for the supplied user ID.
-	targetUserNIDs, err := db.EventStateKeyNIDs(ctx, []string{userID})
+	targetUserNIDs, err := db.EventStateKeyNIDs(ctx, []string{string(senderID)})
 	if err != nil {
 		return false, "", "", nil, fmt.Errorf("r.DB.EventStateKeyNIDs: %w", err)
 	}
-	targetUserNID, targetUserFound := targetUserNIDs[userID]
+	targetUserNID, targetUserFound := targetUserNIDs[string(senderID)]
 	if !targetUserFound {
-		return false, "", "", nil, fmt.Errorf("missing NID for user %q (%+v)", userID, targetUserNIDs)
+		return false, "", "", nil, fmt.Errorf("missing NID for user %q (%+v)", senderID, targetUserNIDs)
 	}
 
 	// Let's see if we have an event active for the user in the room. If
@@ -156,7 +157,7 @@ func IsInvitePending(
 
 	event, err := verImpl.NewEventFromTrustedJSON(eventJSON, false)
 
-	return true, senderUser, userNIDToEventID[senderUserNIDs[0]], event, err
+	return true, spec.SenderID(senderUser), userNIDToEventID[senderUserNIDs[0]], event, err
 }
 
 // GetMembershipsAtState filters the state events to
diff --git a/roomserver/internal/helpers/helpers_test.go b/roomserver/internal/helpers/helpers_test.go
index f1896277e..1cef83df7 100644
--- a/roomserver/internal/helpers/helpers_test.go
+++ b/roomserver/internal/helpers/helpers_test.go
@@ -8,6 +8,7 @@ import (
 	"github.com/matrix-org/dendrite/internal/caching"
 	"github.com/matrix-org/dendrite/internal/sqlutil"
 	"github.com/matrix-org/dendrite/setup/config"
+	"github.com/matrix-org/gomatrixserverlib/spec"
 	"github.com/stretchr/testify/assert"
 
 	"github.com/matrix-org/dendrite/roomserver/types"
@@ -58,12 +59,12 @@ func TestIsInvitePendingWithoutNID(t *testing.T) {
 		}
 
 		// Alice should have no pending invites and should have a NID
-		pendingInvite, _, _, _, err := IsInvitePending(context.Background(), db, room.ID, alice.ID)
+		pendingInvite, _, _, _, err := IsInvitePending(context.Background(), db, room.ID, spec.SenderID(alice.ID))
 		assert.NoError(t, err, "failed to get pending invites")
 		assert.False(t, pendingInvite, "unexpected pending invite")
 
 		// Bob should have no pending invites and receive a new NID
-		pendingInvite, _, _, _, err = IsInvitePending(context.Background(), db, room.ID, bob.ID)
+		pendingInvite, _, _, _, err = IsInvitePending(context.Background(), db, room.ID, spec.SenderID(bob.ID))
 		assert.NoError(t, err, "failed to get pending invites")
 		assert.False(t, pendingInvite, "unexpected pending invite")
 	})
diff --git a/roomserver/internal/input/input_membership.go b/roomserver/internal/input/input_membership.go
index 98d7d13b1..54cad14f7 100644
--- a/roomserver/internal/input/input_membership.go
+++ b/roomserver/internal/input/input_membership.go
@@ -161,9 +161,10 @@ func updateToJoinMembership(
 			Type: api.OutputTypeRetireInviteEvent,
 			RetireInviteEvent: &api.OutputRetireInviteEvent{
 				EventID:          eventID,
+				RoomID:           add.RoomID(),
 				Membership:       spec.Join,
 				RetiredByEventID: add.EventID(),
-				TargetUserID:     *add.StateKey(),
+				TargetSenderID:   spec.SenderID(*add.StateKey()),
 			},
 		})
 	}
@@ -187,9 +188,10 @@ func updateToLeaveMembership(
 			Type: api.OutputTypeRetireInviteEvent,
 			RetireInviteEvent: &api.OutputRetireInviteEvent{
 				EventID:          eventID,
+				RoomID:           add.RoomID(),
 				Membership:       newMembership,
 				RetiredByEventID: add.EventID(),
-				TargetUserID:     *add.StateKey(),
+				TargetSenderID:   spec.SenderID(*add.StateKey()),
 			},
 		})
 	}
diff --git a/roomserver/internal/perform/perform_admin.go b/roomserver/internal/perform/perform_admin.go
index eeb1ac406..a9ce63043 100644
--- a/roomserver/internal/perform/perform_admin.go
+++ b/roomserver/internal/perform/perform_admin.go
@@ -149,11 +149,11 @@ func (r *Admin) PerformAdminEvacuateUser(
 	ctx context.Context,
 	userID string,
 ) (affected []string, err error) {
-	_, domain, err := gomatrixserverlib.SplitID('@', userID)
+	fullUserID, err := spec.NewUserID(userID, true)
 	if err != nil {
 		return nil, err
 	}
-	if !r.Cfg.Matrix.IsLocalServerName(domain) {
+	if !r.Cfg.Matrix.IsLocalServerName(fullUserID.Domain()) {
 		return nil, fmt.Errorf("can only evacuate local users using this endpoint")
 	}
 
@@ -170,9 +170,13 @@ func (r *Admin) PerformAdminEvacuateUser(
 	allRooms := append(roomIDs, inviteRoomIDs...)
 	affected = make([]string, 0, len(allRooms))
 	for _, roomID := range allRooms {
+		senderID, err := r.Queryer.QuerySenderIDForUser(ctx, roomID, *fullUserID)
+		if err != nil {
+			return nil, err
+		}
 		leaveReq := &api.PerformLeaveRequest{
 			RoomID: roomID,
-			UserID: userID,
+			Leaver: api.SenderUserIDPair{SenderID: senderID, UserID: *fullUserID},
 		}
 		leaveRes := &api.PerformLeaveResponse{}
 		outputEvents, err := r.Leaver.PerformLeave(ctx, leaveReq, leaveRes)
diff --git a/roomserver/internal/perform/perform_join.go b/roomserver/internal/perform/perform_join.go
index d41cc214b..0052483ab 100644
--- a/roomserver/internal/perform/perform_join.go
+++ b/roomserver/internal/perform/perform_join.go
@@ -203,7 +203,7 @@ func (r *Joiner) performJoinRoomByID(
 		req.Content = map[string]interface{}{}
 	}
 	req.Content["membership"] = spec.Join
-	if authorisedVia, aerr := r.populateAuthorisedViaUserForRestrictedJoin(ctx, req); aerr != nil {
+	if authorisedVia, aerr := r.populateAuthorisedViaUserForRestrictedJoin(ctx, req, senderID); aerr != nil {
 		return "", "", aerr
 	} else if authorisedVia != "" {
 		req.Content["join_authorised_via_users_server"] = authorisedVia
@@ -226,17 +226,17 @@ func (r *Joiner) performJoinRoomByID(
 
 	// Force a federated join if we're dealing with a pending invite
 	// and we aren't in the room.
-	isInvitePending, inviteSender, _, inviteEvent, err := helpers.IsInvitePending(ctx, r.DB, req.RoomIDOrAlias, req.UserID)
+	isInvitePending, inviteSender, _, inviteEvent, err := helpers.IsInvitePending(ctx, r.DB, req.RoomIDOrAlias, senderID)
 	if err == nil && !serverInRoom && isInvitePending {
-		_, inviterDomain, ierr := gomatrixserverlib.SplitID('@', inviteSender)
-		if ierr != nil {
-			return "", "", fmt.Errorf("gomatrixserverlib.SplitID: %w", err)
+		inviter, queryErr := r.RSAPI.QueryUserIDForSender(ctx, req.RoomIDOrAlias, inviteSender)
+		if queryErr != nil {
+			return "", "", fmt.Errorf("r.RSAPI.QueryUserIDForSender: %w", queryErr)
 		}
 
 		// If we were invited by someone from another server then we can
 		// assume they are in the room so we can join via them.
-		if !r.Cfg.Matrix.IsLocalServerName(inviterDomain) {
-			req.ServerNames = append(req.ServerNames, inviterDomain)
+		if inviter != nil && !r.Cfg.Matrix.IsLocalServerName(inviter.Domain()) {
+			req.ServerNames = append(req.ServerNames, inviter.Domain())
 			forceFederatedJoin = true
 			memberEvent := gjson.Parse(string(inviteEvent.JSON()))
 			// only set unsigned if we've got a content.membership, which we _should_
@@ -299,8 +299,8 @@ func (r *Joiner) performJoinRoomByID(
 		// fail if we can't find the existing membership) because there
 		// is really no harm in just sending another membership event.
 		membershipReq := &api.QueryMembershipForUserRequest{
-			RoomID: req.RoomIDOrAlias,
-			UserID: userID.String(),
+			RoomID:   req.RoomIDOrAlias,
+			SenderID: senderID,
 		}
 		membershipRes := &api.QueryMembershipForUserResponse{}
 		_ = r.Queryer.QueryMembershipForUser(ctx, membershipReq, membershipRes)
@@ -376,15 +376,12 @@ func (r *Joiner) performFederatedJoinRoomByID(
 func (r *Joiner) populateAuthorisedViaUserForRestrictedJoin(
 	ctx context.Context,
 	joinReq *rsAPI.PerformJoinRequest,
+	senderID spec.SenderID,
 ) (string, error) {
 	roomID, err := spec.NewRoomID(joinReq.RoomIDOrAlias)
 	if err != nil {
 		return "", err
 	}
-	userID, err := spec.NewUserID(joinReq.UserID, true)
-	if err != nil {
-		return "", err
-	}
 
-	return r.Queryer.QueryRestrictedJoinAllowed(ctx, *roomID, *userID)
+	return r.Queryer.QueryRestrictedJoinAllowed(ctx, *roomID, senderID)
 }
diff --git a/roomserver/internal/perform/perform_leave.go b/roomserver/internal/perform/perform_leave.go
index 094537f8b..8fa324865 100644
--- a/roomserver/internal/perform/perform_leave.go
+++ b/roomserver/internal/perform/perform_leave.go
@@ -53,16 +53,12 @@ func (r *Leaver) PerformLeave(
 	req *api.PerformLeaveRequest,
 	res *api.PerformLeaveResponse,
 ) ([]api.OutputEvent, error) {
-	_, domain, err := gomatrixserverlib.SplitID('@', req.UserID)
-	if err != nil {
-		return nil, fmt.Errorf("supplied user ID %q in incorrect format", req.UserID)
-	}
-	if !r.Cfg.Matrix.IsLocalServerName(domain) {
-		return nil, fmt.Errorf("user %q does not belong to this homeserver", req.UserID)
+	if !r.Cfg.Matrix.IsLocalServerName(req.Leaver.UserID.Domain()) {
+		return nil, fmt.Errorf("user %q does not belong to this homeserver", req.Leaver.UserID.String())
 	}
 	logger := logrus.WithContext(ctx).WithFields(logrus.Fields{
 		"room_id": req.RoomID,
-		"user_id": req.UserID,
+		"user_id": req.Leaver.UserID.String(),
 	})
 	logger.Info("User requested to leave join")
 	if strings.HasPrefix(req.RoomID, "!") {
@@ -84,19 +80,20 @@ func (r *Leaver) performLeaveRoomByID(
 ) ([]api.OutputEvent, error) {
 	// If there's an invite outstanding for the room then respond to
 	// that.
-	isInvitePending, senderUser, eventID, _, err := helpers.IsInvitePending(ctx, r.DB, req.RoomID, req.UserID)
+	isInvitePending, senderUser, eventID, _, err := helpers.IsInvitePending(ctx, r.DB, req.RoomID, req.Leaver.SenderID)
 	if err == nil && isInvitePending {
-		_, senderDomain, serr := gomatrixserverlib.SplitID('@', senderUser)
-		if serr != nil {
-			return nil, fmt.Errorf("sender %q is invalid", senderUser)
+		sender, serr := r.RSAPI.QueryUserIDForSender(ctx, req.RoomID, senderUser)
+		if serr != nil || sender == nil {
+			return nil, fmt.Errorf("sender %q has no matching userID", senderUser)
 		}
-		if !r.Cfg.Matrix.IsLocalServerName(senderDomain) {
-			return r.performFederatedRejectInvite(ctx, req, res, senderUser, eventID)
+		inviteSender := api.SenderUserIDPair{SenderID: senderUser, UserID: *sender}
+		if !r.Cfg.Matrix.IsLocalServerName(sender.Domain()) {
+			return r.performFederatedRejectInvite(ctx, req, res, inviteSender.UserID, eventID)
 		}
 		// check that this is not a "server notice room"
 		accData := &userapi.QueryAccountDataResponse{}
 		if err = r.UserAPI.QueryAccountData(ctx, &userapi.QueryAccountDataRequest{
-			UserID:   req.UserID,
+			UserID:   req.Leaver.UserID.String(),
 			RoomID:   req.RoomID,
 			DataType: "m.tag",
 		}, accData); err != nil {
@@ -127,7 +124,7 @@ func (r *Leaver) performLeaveRoomByID(
 		StateToFetch: []gomatrixserverlib.StateKeyTuple{
 			{
 				EventType: spec.MRoomMember,
-				StateKey:  req.UserID,
+				StateKey:  string(req.Leaver.SenderID),
 			},
 		},
 	}
@@ -141,26 +138,18 @@ func (r *Leaver) performLeaveRoomByID(
 
 	// Now let's see if the user is in the room.
 	if len(latestRes.StateEvents) == 0 {
-		return nil, fmt.Errorf("user %q is not a member of room %q", req.UserID, req.RoomID)
+		return nil, fmt.Errorf("user %q is not a member of room %q", req.Leaver.UserID.String(), req.RoomID)
 	}
 	membership, err := latestRes.StateEvents[0].Membership()
 	if err != nil {
 		return nil, fmt.Errorf("error getting membership: %w", err)
 	}
 	if membership != spec.Join && membership != spec.Invite {
-		return nil, fmt.Errorf("user %q is not joined to the room (membership is %q)", req.UserID, membership)
+		return nil, fmt.Errorf("user %q is not joined to the room (membership is %q)", req.Leaver.UserID.String(), membership)
 	}
 
 	// Prepare the template for the leave event.
-	fullUserID, err := spec.NewUserID(req.UserID, true)
-	if err != nil {
-		return nil, err
-	}
-	senderID, err := r.RSAPI.QuerySenderIDForUser(ctx, req.RoomID, *fullUserID)
-	if err != nil {
-		return nil, err
-	}
-	senderIDString := string(senderID)
+	senderIDString := string(req.Leaver.SenderID)
 	proto := gomatrixserverlib.ProtoEvent{
 		Type:     spec.MRoomMember,
 		SenderID: senderIDString,
@@ -175,16 +164,13 @@ func (r *Leaver) performLeaveRoomByID(
 		return nil, fmt.Errorf("eb.SetUnsigned: %w", err)
 	}
 
-	// Get the sender domain.
-	senderDomain := fullUserID.Domain()
-
 	// We know that the user is in the room at this point so let's build
 	// a leave event.
 	// TODO: Check what happens if the room exists on the server
 	// but everyone has since left. I suspect it does the wrong thing.
 
 	var buildRes rsAPI.QueryLatestEventsAndStateResponse
-	identity, err := r.Cfg.Matrix.SigningIdentityFor(senderDomain)
+	identity, err := r.Cfg.Matrix.SigningIdentityFor(req.Leaver.UserID.Domain())
 	if err != nil {
 		return nil, fmt.Errorf("SigningIdentityFor: %w", err)
 	}
@@ -201,8 +187,8 @@ func (r *Leaver) performLeaveRoomByID(
 			{
 				Kind:         api.KindNew,
 				Event:        event,
-				Origin:       senderDomain,
-				SendAsServer: string(senderDomain),
+				Origin:       req.Leaver.UserID.Domain(),
+				SendAsServer: string(req.Leaver.UserID.Domain()),
 			},
 		},
 	}
@@ -219,21 +205,16 @@ func (r *Leaver) performFederatedRejectInvite(
 	ctx context.Context,
 	req *api.PerformLeaveRequest,
 	res *api.PerformLeaveResponse, // nolint:unparam
-	senderUser, eventID string,
+	inviteSender spec.UserID, eventID string,
 ) ([]api.OutputEvent, error) {
-	_, domain, err := gomatrixserverlib.SplitID('@', senderUser)
-	if err != nil {
-		return nil, fmt.Errorf("user ID %q invalid: %w", senderUser, err)
-	}
-
 	// Ask the federation sender to perform a federated leave for us.
 	leaveReq := fsAPI.PerformLeaveRequest{
 		RoomID:      req.RoomID,
-		UserID:      req.UserID,
-		ServerNames: []spec.ServerName{domain},
+		UserID:      req.Leaver.UserID.String(),
+		ServerNames: []spec.ServerName{inviteSender.Domain()},
 	}
 	leaveRes := fsAPI.PerformLeaveResponse{}
-	if err = r.FSAPI.PerformLeave(ctx, &leaveReq, &leaveRes); err != nil {
+	if err := r.FSAPI.PerformLeave(ctx, &leaveReq, &leaveRes); err != nil {
 		// failures in PerformLeave should NEVER stop us from telling other components like the
 		// sync API that the invite was withdrawn. Otherwise we can end up with stuck invites.
 		util.GetLogger(ctx).WithError(err).Errorf("failed to PerformLeave, still retiring invite event")
@@ -244,7 +225,7 @@ func (r *Leaver) performFederatedRejectInvite(
 		util.GetLogger(ctx).WithError(err).Errorf("failed to get RoomInfo, still retiring invite event")
 	}
 
-	updater, err := r.DB.MembershipUpdater(ctx, req.RoomID, req.UserID, true, info.RoomVersion)
+	updater, err := r.DB.MembershipUpdater(ctx, req.RoomID, string(req.Leaver.SenderID), true, info.RoomVersion)
 	if err != nil {
 		util.GetLogger(ctx).WithError(err).Errorf("failed to get MembershipUpdater, still retiring invite event")
 	}
@@ -267,9 +248,10 @@ func (r *Leaver) performFederatedRejectInvite(
 		{
 			Type: api.OutputTypeRetireInviteEvent,
 			RetireInviteEvent: &api.OutputRetireInviteEvent{
-				EventID:      eventID,
-				Membership:   "leave",
-				TargetUserID: req.UserID,
+				EventID:        eventID,
+				RoomID:         req.RoomID,
+				Membership:     "leave",
+				TargetSenderID: req.Leaver.SenderID,
 			},
 		},
 	}, nil
diff --git a/roomserver/internal/query/query.go b/roomserver/internal/query/query.go
index 08af41c1e..511c149d8 100644
--- a/roomserver/internal/query/query.go
+++ b/roomserver/internal/query/query.go
@@ -48,7 +48,7 @@ type Queryer struct {
 	Cfg               *config.Dendrite
 }
 
-func (r *Queryer) RestrictedRoomJoinInfo(ctx context.Context, roomID spec.RoomID, userID spec.UserID, localServerName spec.ServerName) (*gomatrixserverlib.RestrictedRoomJoinInfo, error) {
+func (r *Queryer) RestrictedRoomJoinInfo(ctx context.Context, roomID spec.RoomID, senderID spec.SenderID, localServerName spec.ServerName) (*gomatrixserverlib.RestrictedRoomJoinInfo, error) {
 	roomInfo, err := r.QueryRoomInfo(ctx, roomID)
 	if err != nil || roomInfo == nil || roomInfo.IsStub() {
 		return nil, err
@@ -64,7 +64,7 @@ func (r *Queryer) RestrictedRoomJoinInfo(ctx context.Context, roomID spec.RoomID
 		return nil, fmt.Errorf("InternalServerError: Failed to query room: %w", err)
 	}
 
-	userJoinedToRoom, err := r.UserJoinedToRoom(ctx, types.RoomNID(roomInfo.RoomNID), userID)
+	userJoinedToRoom, err := r.UserJoinedToRoom(ctx, types.RoomNID(roomInfo.RoomNID), senderID)
 	if err != nil {
 		util.GetLogger(ctx).WithError(err).Error("rsAPI.UserJoinedToRoom failed")
 		return nil, fmt.Errorf("InternalServerError: %w", err)
@@ -236,7 +236,7 @@ func (r *Queryer) QueryMembershipForUser(
 	}
 	response.RoomExists = true
 
-	membershipEventNID, stillInRoom, isRoomforgotten, err := r.DB.GetMembership(ctx, info.RoomNID, request.UserID)
+	membershipEventNID, stillInRoom, isRoomforgotten, err := r.DB.GetMembership(ctx, info.RoomNID, request.SenderID)
 	if err != nil {
 		return err
 	}
@@ -373,7 +373,7 @@ func (r *Queryer) QueryMembershipsForRoom(
 	// If no sender is specified then we will just return the entire
 	// set of memberships for the room, regardless of whether a specific
 	// user is allowed to see them or not.
-	if request.Sender == "" {
+	if request.SenderID == "" {
 		var events []types.Event
 		var eventNIDs []types.EventNID
 		eventNIDs, err = r.DB.GetMembershipEventNIDsForRoom(ctx, info.RoomNID, request.JoinedOnly, request.LocalOnly)
@@ -396,7 +396,7 @@ func (r *Queryer) QueryMembershipsForRoom(
 		return nil
 	}
 
-	membershipEventNID, stillInRoom, isRoomforgotten, err := r.DB.GetMembership(ctx, info.RoomNID, request.Sender)
+	membershipEventNID, stillInRoom, isRoomforgotten, err := r.DB.GetMembership(ctx, info.RoomNID, request.SenderID)
 	if err != nil {
 		return err
 	}
@@ -903,8 +903,8 @@ func (r *Queryer) QueryAuthChain(ctx context.Context, req *api.QueryAuthChainReq
 	return nil
 }
 
-func (r *Queryer) InvitePending(ctx context.Context, roomID spec.RoomID, userID spec.UserID) (bool, error) {
-	pending, _, _, _, err := helpers.IsInvitePending(ctx, r.DB, roomID.String(), userID.String())
+func (r *Queryer) InvitePending(ctx context.Context, roomID spec.RoomID, senderID spec.SenderID) (bool, error) {
+	pending, _, _, _, err := helpers.IsInvitePending(ctx, r.DB, roomID.String(), senderID)
 	return pending, err
 }
 
@@ -920,8 +920,8 @@ func (r *Queryer) CurrentStateEvent(ctx context.Context, roomID spec.RoomID, eve
 	return res, err
 }
 
-func (r *Queryer) UserJoinedToRoom(ctx context.Context, roomNID types.RoomNID, userID spec.UserID) (bool, error) {
-	_, isIn, _, err := r.DB.GetMembership(ctx, roomNID, userID.String())
+func (r *Queryer) UserJoinedToRoom(ctx context.Context, roomNID types.RoomNID, senderID spec.SenderID) (bool, error) {
+	_, isIn, _, err := r.DB.GetMembership(ctx, roomNID, senderID)
 	return isIn, err
 }
 
@@ -951,7 +951,7 @@ func (r *Queryer) LocallyJoinedUsers(ctx context.Context, roomVersion gomatrixse
 }
 
 // nolint:gocyclo
-func (r *Queryer) QueryRestrictedJoinAllowed(ctx context.Context, roomID spec.RoomID, userID spec.UserID) (string, error) {
+func (r *Queryer) QueryRestrictedJoinAllowed(ctx context.Context, roomID spec.RoomID, senderID spec.SenderID) (string, error) {
 	// Look up if we know anything about the room. If it doesn't exist
 	// or is a stub entry then we can't do anything.
 	roomInfo, err := r.DB.RoomInfo(ctx, roomID.String())
@@ -966,7 +966,7 @@ func (r *Queryer) QueryRestrictedJoinAllowed(ctx context.Context, roomID spec.Ro
 		return "", err
 	}
 
-	return verImpl.CheckRestrictedJoin(ctx, r.Cfg.Global.ServerName, &api.JoinRoomQuerier{Roomserver: r}, roomID, userID)
+	return verImpl.CheckRestrictedJoin(ctx, r.Cfg.Global.ServerName, &api.JoinRoomQuerier{Roomserver: r}, roomID, senderID)
 }
 
 func (r *Queryer) QuerySenderIDForUser(ctx context.Context, roomID string, userID spec.UserID) (spec.SenderID, error) {
diff --git a/roomserver/roomserver_test.go b/roomserver/roomserver_test.go
index 5e6ba7d4e..73460ffd4 100644
--- a/roomserver/roomserver_test.go
+++ b/roomserver/roomserver_test.go
@@ -722,7 +722,7 @@ func TestQueryRestrictedJoinAllowed(t *testing.T) {
 
 				roomID, _ := spec.NewRoomID(testRoom.ID)
 				userID, _ := spec.NewUserID(bob.ID, true)
-				got, err := rsAPI.QueryRestrictedJoinAllowed(processCtx.Context(), *roomID, *userID)
+				got, err := rsAPI.QueryRestrictedJoinAllowed(processCtx.Context(), *roomID, spec.SenderID(userID.String()))
 				if tc.wantError && err == nil {
 					t.Fatal("expected error, got none")
 				}
diff --git a/roomserver/storage/interface.go b/roomserver/storage/interface.go
index 523cc361a..e9f952490 100644
--- a/roomserver/storage/interface.go
+++ b/roomserver/storage/interface.go
@@ -129,7 +129,7 @@ type Database interface {
 	// in this room, along a boolean set to true if the user is still in this room,
 	// false if not.
 	// Returns an error if there was a problem talking to the database.
-	GetMembership(ctx context.Context, roomNID types.RoomNID, requestSenderUserID string) (membershipEventNID types.EventNID, stillInRoom, isRoomForgotten bool, err error)
+	GetMembership(ctx context.Context, roomNID types.RoomNID, requestSenderID spec.SenderID) (membershipEventNID types.EventNID, stillInRoom, isRoomForgotten bool, err error)
 	// Lookup the membership event numeric IDs for all user that are or have
 	// been members of a given room. Only lookup events of "join" membership if
 	// joinOnly is set to true.
diff --git a/roomserver/storage/shared/storage.go b/roomserver/storage/shared/storage.go
index f2f842357..30bb4dedc 100644
--- a/roomserver/storage/shared/storage.go
+++ b/roomserver/storage/shared/storage.go
@@ -485,10 +485,10 @@ func (d *Database) RemoveRoomAlias(ctx context.Context, alias string) error {
 	})
 }
 
-func (d *Database) GetMembership(ctx context.Context, roomNID types.RoomNID, requestSenderUserID string) (membershipEventNID types.EventNID, stillInRoom, isRoomforgotten bool, err error) {
+func (d *Database) GetMembership(ctx context.Context, roomNID types.RoomNID, requestSenderID spec.SenderID) (membershipEventNID types.EventNID, stillInRoom, isRoomforgotten bool, err error) {
 	var requestSenderUserNID types.EventStateKeyNID
 	err = d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
-		requestSenderUserNID, err = d.assignStateKeyNID(ctx, txn, requestSenderUserID)
+		requestSenderUserNID, err = d.assignStateKeyNID(ctx, txn, string(requestSenderID))
 		return err
 	})
 	if err != nil {
diff --git a/setup/mscs/msc2836/msc2836.go b/setup/mscs/msc2836/msc2836.go
index 47eb544ea..fdf3d0799 100644
--- a/setup/mscs/msc2836/msc2836.go
+++ b/setup/mscs/msc2836/msc2836.go
@@ -155,6 +155,7 @@ type reqCtx struct {
 	db          Database
 	req         *EventRelationshipRequest
 	userID      string
+	senderID    spec.SenderID
 	roomVersion gomatrixserverlib.RoomVersion
 
 	// federated request args
@@ -173,10 +174,25 @@ func eventRelationshipHandler(db Database, rsAPI roomserver.RoomserverInternalAP
 				JSON: spec.BadJSON(fmt.Sprintf("invalid json: %s", err)),
 			}
 		}
+		userID, err := spec.NewUserID(device.UserID, true)
+		if err != nil {
+			return util.JSONResponse{
+				Code: 400,
+				JSON: spec.BadJSON(fmt.Sprintf("invalid json: %s", err)),
+			}
+		}
+		senderID, err := rsAPI.QuerySenderIDForUser(req.Context(), relation.RoomID, *userID)
+		if err != nil {
+			return util.JSONResponse{
+				Code: 400,
+				JSON: spec.BadJSON(fmt.Sprintf("invalid json: %s", err)),
+			}
+		}
 		rc := reqCtx{
 			ctx:                req.Context(),
 			req:                relation,
 			userID:             device.UserID,
+			senderID:           senderID,
 			rsAPI:              rsAPI,
 			fsAPI:              fsAPI,
 			isFederatedRequest: false,
@@ -337,8 +353,8 @@ func (rc *reqCtx) fetchUnknownEvent(eventID, roomID string) *types.HeaderedEvent
 	// check the user is joined to that room
 	var queryMemRes roomserver.QueryMembershipForUserResponse
 	err = rc.rsAPI.QueryMembershipForUser(rc.ctx, &roomserver.QueryMembershipForUserRequest{
-		RoomID: roomID,
-		UserID: rc.userID,
+		RoomID:   roomID,
+		SenderID: rc.senderID,
 	}, &queryMemRes)
 	if err != nil {
 		logger.WithError(err).Warn("failed to query membership for user in room")
@@ -538,8 +554,8 @@ func (rc *reqCtx) authorisedToSeeEvent(event *types.HeaderedEvent) bool {
 	// TODO: This does not honour m.room.create content
 	var queryMembershipRes roomserver.QueryMembershipForUserResponse
 	err := rc.rsAPI.QueryMembershipForUser(rc.ctx, &roomserver.QueryMembershipForUserRequest{
-		RoomID: event.RoomID(),
-		UserID: rc.userID,
+		RoomID:   event.RoomID(),
+		SenderID: rc.senderID,
 	}, &queryMembershipRes)
 	if err != nil {
 		util.GetLogger(rc.ctx).WithError(err).Error("authorisedToSeeEvent: failed to QueryMembershipForUser")
diff --git a/setup/mscs/msc2836/msc2836_test.go b/setup/mscs/msc2836/msc2836_test.go
index 551d7ad45..040e6d958 100644
--- a/setup/mscs/msc2836/msc2836_test.go
+++ b/setup/mscs/msc2836/msc2836_test.go
@@ -529,6 +529,10 @@ func (r *testRoomserverAPI) QueryUserIDForSender(ctx context.Context, roomID str
 	return spec.NewUserID(string(senderID), true)
 }
 
+func (r *testRoomserverAPI) QuerySenderIDForUser(ctx context.Context, roomID string, userID spec.UserID) (spec.SenderID, error) {
+	return spec.SenderID(userID.String()), nil
+}
+
 func (r *testRoomserverAPI) QueryEventsByID(ctx context.Context, req *roomserver.QueryEventsByIDRequest, res *roomserver.QueryEventsByIDResponse) error {
 	for _, eventID := range req.EventIDs {
 		ev := r.events[eventID]
@@ -540,7 +544,7 @@ func (r *testRoomserverAPI) QueryEventsByID(ctx context.Context, req *roomserver
 }
 
 func (r *testRoomserverAPI) QueryMembershipForUser(ctx context.Context, req *roomserver.QueryMembershipForUserRequest, res *roomserver.QueryMembershipForUserResponse) error {
-	rooms := r.userToJoinedRooms[req.UserID]
+	rooms := r.userToJoinedRooms[string(req.SenderID)]
 	for _, roomID := range rooms {
 		if roomID == req.RoomID {
 			res.IsInRoom = true
diff --git a/syncapi/consumers/roomserver.go b/syncapi/consumers/roomserver.go
index 3cd0e77bc..c5f2db9c8 100644
--- a/syncapi/consumers/roomserver.go
+++ b/syncapi/consumers/roomserver.go
@@ -454,7 +454,16 @@ func (s *OutputRoomEventConsumer) onRetireInviteEvent(
 
 	// Notify any active sync requests that the invite has been retired.
 	s.inviteStream.Advance(pduPos)
-	s.notifier.OnNewInvite(types.StreamingToken{InvitePosition: pduPos}, msg.TargetUserID)
+	userID, err := s.rsAPI.QueryUserIDForSender(ctx, msg.RoomID, msg.TargetSenderID)
+	if err != nil || userID == nil {
+		log.WithFields(log.Fields{
+			"event_id":   msg.EventID,
+			"sender_id":  msg.TargetSenderID,
+			log.ErrorKey: err,
+		}).Errorf("failed to find userID for sender")
+		return
+	}
+	s.notifier.OnNewInvite(types.StreamingToken{InvitePosition: pduPos}, userID.String())
 }
 
 func (s *OutputRoomEventConsumer) onNewPeek(
diff --git a/syncapi/routing/context.go b/syncapi/routing/context.go
index 144baff1e..1a8d33e38 100644
--- a/syncapi/routing/context.go
+++ b/syncapi/routing/context.go
@@ -85,9 +85,23 @@ func Context(
 		*filter.Rooms = append(*filter.Rooms, roomID)
 	}
 
+	userID, err := spec.NewUserID(device.UserID, true)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: spec.InvalidParam("Device UserID is invalid"),
+		}
+	}
+	senderID, err := rsAPI.QuerySenderIDForUser(req.Context(), roomID, *userID)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusNotFound,
+			JSON: spec.Unknown("SenderID for this device is unknown"),
+		}
+	}
 	ctx := req.Context()
 	membershipRes := roomserver.QueryMembershipForUserResponse{}
-	membershipReq := roomserver.QueryMembershipForUserRequest{UserID: device.UserID, RoomID: roomID}
+	membershipReq := roomserver.QueryMembershipForUserRequest{SenderID: senderID, RoomID: roomID}
 	if err = rsAPI.QueryMembershipForUser(ctx, &membershipReq, &membershipRes); err != nil {
 		logrus.WithError(err).Error("unable to query membership")
 		return util.JSONResponse{
diff --git a/syncapi/routing/memberships.go b/syncapi/routing/memberships.go
index 813167a5e..bd2b37a14 100644
--- a/syncapi/routing/memberships.go
+++ b/syncapi/routing/memberships.go
@@ -59,14 +59,28 @@ func GetMemberships(
 	syncDB storage.Database, rsAPI api.SyncRoomserverAPI,
 	joinedOnly bool, membership, notMembership *string, at string,
 ) util.JSONResponse {
+	userID, err := spec.NewUserID(device.UserID, true)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: spec.InvalidParam("Device UserID is invalid"),
+		}
+	}
+	senderID, err := rsAPI.QuerySenderIDForUser(req.Context(), roomID, *userID)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusNotFound,
+			JSON: spec.Unknown("SenderID for this device is unknown"),
+		}
+	}
 	queryReq := api.QueryMembershipForUserRequest{
-		RoomID: roomID,
-		UserID: device.UserID,
+		RoomID:   roomID,
+		SenderID: senderID,
 	}
 
 	var queryRes api.QueryMembershipForUserResponse
-	if err := rsAPI.QueryMembershipForUser(req.Context(), &queryReq, &queryRes); err != nil {
-		util.GetLogger(req.Context()).WithError(err).Error("rsAPI.QueryMembershipsForRoom failed")
+	if queryErr := rsAPI.QueryMembershipForUser(req.Context(), &queryReq, &queryRes); queryErr != nil {
+		util.GetLogger(req.Context()).WithError(queryErr).Error("rsAPI.QueryMembershipsForRoom failed")
 		return util.JSONResponse{
 			Code: http.StatusInternalServerError,
 			JSON: spec.InternalServerError{},
diff --git a/syncapi/routing/messages.go b/syncapi/routing/messages.go
index 781fd53e7..91cf289f2 100644
--- a/syncapi/routing/messages.go
+++ b/syncapi/routing/messages.go
@@ -296,9 +296,17 @@ func OnIncomingMessagesRequest(
 }
 
 func getMembershipForUser(ctx context.Context, roomID, userID string, rsAPI api.SyncRoomserverAPI) (resp api.QueryMembershipForUserResponse, err error) {
+	fullUserID, err := spec.NewUserID(userID, true)
+	if err != nil {
+		return resp, err
+	}
+	senderID, err := rsAPI.QuerySenderIDForUser(ctx, roomID, *fullUserID)
+	if err != nil {
+		return resp, err
+	}
 	req := api.QueryMembershipForUserRequest{
-		RoomID: roomID,
-		UserID: userID,
+		RoomID:   roomID,
+		SenderID: senderID,
 	}
 	if err := rsAPI.QueryMembershipForUser(ctx, &req, &resp); err != nil {
 		return api.QueryMembershipForUserResponse{}, err