diff --git a/appservice/consumers/roomserver.go b/appservice/consumers/roomserver.go
index 634031fe7..97dd90deb 100644
--- a/appservice/consumers/roomserver.go
+++ b/appservice/consumers/roomserver.go
@@ -233,17 +233,10 @@ func (s *appserviceState) backoffAndPause(err error) error {
 //
 // TODO: This should be cached, see https://github.com/matrix-org/dendrite/issues/1682
 func (s *OutputRoomEventConsumer) appserviceIsInterestedInEvent(ctx context.Context, event *types.HeaderedEvent, appservice *config.ApplicationService) bool {
-	userID, err := event.UserID()
-	if err != nil {
-		log.WithFields(log.Fields{
-			"appservice": appservice.ID,
-			"room_id":    event.RoomID(),
-		}).WithError(err).Errorf("invalid userID")
-	}
 	switch {
 	case appservice.URL == "":
 		return false
-	case appservice.IsInterestedInUserID(userID.String()):
+	case appservice.IsInterestedInUserID(event.SenderID()):
 		return true
 	case appservice.IsInterestedInRoomID(event.RoomID()):
 		return true
diff --git a/clientapi/routing/redaction.go b/clientapi/routing/redaction.go
index 76377a5bd..bd3a79ebc 100644
--- a/clientapi/routing/redaction.go
+++ b/clientapi/routing/redaction.go
@@ -76,14 +76,7 @@ func SendRedaction(
 	// "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
-	userID, err := ev.UserID()
-	if err != nil {
-		return util.JSONResponse{
-			Code: 400,
-			JSON: spec.BadJSON("invalid userID"),
-		}
-	}
-	allowedToRedact := userID.String() == device.UserID
+	allowedToRedact := ev.SenderID() == device.UserID
 	if !allowedToRedact {
 		plEvent := roomserverAPI.GetStateEvent(req.Context(), rsAPI, roomID, gomatrixserverlib.StateKeyTuple{
 			EventType: spec.MRoomPowerLevels,
@@ -126,7 +119,7 @@ func SendRedaction(
 		Type:    spec.MRoomRedaction,
 		Redacts: eventID,
 	}
-	err = proto.SetContent(r)
+	err := proto.SetContent(r)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("proto.SetContent failed")
 		return util.JSONResponse{
diff --git a/federationapi/internal/perform.go b/federationapi/internal/perform.go
index 70fa2b841..960a4461e 100644
--- a/federationapi/internal/perform.go
+++ b/federationapi/internal/perform.go
@@ -509,7 +509,7 @@ func (r *FederationInternalAPI) SendInvite(
 	event gomatrixserverlib.PDU,
 	strippedState []gomatrixserverlib.InviteStrippedState,
 ) (gomatrixserverlib.PDU, error) {
-	originUser, err := event.UserID()
+	_, origin, err := r.cfg.Matrix.SplitLocalID('@', event.SenderID())
 	if err != nil {
 		return nil, err
 	}
@@ -542,7 +542,7 @@ func (r *FederationInternalAPI) SendInvite(
 		return nil, fmt.Errorf("gomatrixserverlib.NewInviteV2Request: %w", err)
 	}
 
-	inviteRes, err := r.federation.SendInviteV2(ctx, originUser.Domain(), destination, inviteReq)
+	inviteRes, err := r.federation.SendInviteV2(ctx, origin, destination, inviteReq)
 	if err != nil {
 		return nil, fmt.Errorf("r.federation.SendInviteV2: failed to send invite: %w", err)
 	}
diff --git a/federationapi/routing/leave.go b/federationapi/routing/leave.go
index 91b05e382..84976901a 100644
--- a/federationapi/routing/leave.go
+++ b/federationapi/routing/leave.go
@@ -224,14 +224,12 @@ func SendLeave(
 	// the request. By this point we've already asserted that the sender
 	// and the state key are equal so we don't need to check both.
 	var serverName spec.ServerName
-	userID, err := event.UserID()
-	if err != nil {
+	if _, serverName, err = gomatrixserverlib.SplitID('@', event.SenderID()); err != nil {
 		return util.JSONResponse{
-			Code: http.StatusBadRequest,
+			Code: http.StatusForbidden,
 			JSON: spec.Forbidden("The sender of the join is invalid"),
 		}
-	}
-	if userID.Domain() != request.Origin() {
+	} else if serverName != request.Origin() {
 		return util.JSONResponse{
 			Code: http.StatusForbidden,
 			JSON: spec.Forbidden("The sender does not match the server that originated the request"),
diff --git a/go.mod b/go.mod
index 88aaf7f4a..71e6ffc7a 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 v0.0.0-20230601235030-c4138953b254
+	github.com/matrix-org/gomatrixserverlib v0.0.0-20230602163838-69e05dbabdad
 	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 fc1293a29..565057b44 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 v0.0.0-20230601235030-c4138953b254 h1:javi7tINJfP86mdYeVg7IzDmeRLeaLA0kRzIbEZlK/I=
-github.com/matrix-org/gomatrixserverlib v0.0.0-20230601235030-c4138953b254/go.mod h1:H9V9N3Uqn1bBJqYJNGK1noqtgJTaCEhtTdcH/mp50uU=
+github.com/matrix-org/gomatrixserverlib v0.0.0-20230602163838-69e05dbabdad h1:l+mNyh4S3v0z320VOFuTIGZLjCAeTenVjYBiUNTZm/o=
+github.com/matrix-org/gomatrixserverlib v0.0.0-20230602163838-69e05dbabdad/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/internal/alias.go b/roomserver/internal/alias.go
index 407f4014f..0951172a0 100644
--- a/roomserver/internal/alias.go
+++ b/roomserver/internal/alias.go
@@ -173,7 +173,7 @@ func (r *RoomserverInternalAPI) RemoveRoomAlias(
 			}
 
 			sender := request.UserID
-			if sender != ev.SenderID() {
+			if request.UserID != ev.SenderID() {
 				sender = ev.SenderID()
 			}
 
diff --git a/roomserver/internal/input/input_events.go b/roomserver/internal/input/input_events.go
index 52051f7a4..e203ebf3a 100644
--- a/roomserver/internal/input/input_events.go
+++ b/roomserver/internal/input/input_events.go
@@ -128,7 +128,7 @@ func (r *Inputer) processRoomEvent(
 	if roomInfo == nil && !isCreateEvent {
 		return fmt.Errorf("room %s does not exist for event %s", event.RoomID(), event.EventID())
 	}
-	sender, err := event.UserID()
+	_, senderDomain, err := gomatrixserverlib.SplitID('@', event.SenderID())
 	if err != nil {
 		return fmt.Errorf("event has invalid sender %q", event.SenderID())
 	}
@@ -193,9 +193,9 @@ func (r *Inputer) processRoomEvent(
 			serverRes.ServerNames = append(serverRes.ServerNames, input.Origin)
 			delete(servers, input.Origin)
 		}
-		if sender.Domain() != input.Origin && sender.Domain() != r.Cfg.Matrix.ServerName {
-			serverRes.ServerNames = append(serverRes.ServerNames, sender.Domain())
-			delete(servers, sender.Domain())
+		if senderDomain != input.Origin && senderDomain != r.Cfg.Matrix.ServerName {
+			serverRes.ServerNames = append(serverRes.ServerNames, senderDomain)
+			delete(servers, senderDomain)
 		}
 		for server := range servers {
 			serverRes.ServerNames = append(serverRes.ServerNames, server)
@@ -451,7 +451,7 @@ func (r *Inputer) processRoomEvent(
 	}
 
 	// Handle remote room upgrades, e.g. remove published room
-	if event.Type() == "m.room.tombstone" && event.StateKeyEquals("") && !r.Cfg.Matrix.IsLocalServerName(sender.Domain()) {
+	if event.Type() == "m.room.tombstone" && event.StateKeyEquals("") && !r.Cfg.Matrix.IsLocalServerName(senderDomain) {
 		if err = r.handleRemoteRoomUpgrade(ctx, event); err != nil {
 			return fmt.Errorf("failed to handle remote room upgrade: %w", err)
 		}
diff --git a/roomserver/internal/perform/perform_backfill.go b/roomserver/internal/perform/perform_backfill.go
index e9318235f..9b6d7f678 100644
--- a/roomserver/internal/perform/perform_backfill.go
+++ b/roomserver/internal/perform/perform_backfill.go
@@ -484,11 +484,9 @@ FindSuccessor:
 	// Store the server names in a temporary map to avoid duplicates.
 	serverSet := make(map[spec.ServerName]bool)
 	for _, event := range memberEvents {
-		sender, err := event.UserID()
-		if err != nil {
-			continue
+		if _, senderDomain, err := gomatrixserverlib.SplitID('@', event.SenderID()); err == nil {
+			serverSet[senderDomain] = true
 		}
-		serverSet[sender.Domain()] = true
 	}
 	var servers []spec.ServerName
 	for server := range serverSet {
diff --git a/roomserver/internal/perform/perform_invite.go b/roomserver/internal/perform/perform_invite.go
index 34984eea6..bb41e0dfc 100644
--- a/roomserver/internal/perform/perform_invite.go
+++ b/roomserver/internal/perform/perform_invite.go
@@ -125,7 +125,7 @@ func (r *Inviter) PerformInvite(
 ) error {
 	event := req.Event
 
-	sender, err := event.UserID()
+	sender, err := spec.NewUserID(event.SenderID(), true)
 	if err != nil {
 		return spec.InvalidParam("The user ID is invalid")
 	}
diff --git a/roomserver/storage/shared/storage.go b/roomserver/storage/shared/storage.go
index 78cc15c91..1ee436f99 100644
--- a/roomserver/storage/shared/storage.go
+++ b/roomserver/storage/shared/storage.go
@@ -988,14 +988,8 @@ func (d *EventDatabase) MaybeRedactEvent(
 			return nil
 		}
 
-		sender1, err := redactedEvent.UserID()
-		if err != nil {
-			return err
-		}
-		sender2, err := redactionEvent.UserID()
-		if err != nil {
-			return err
-		}
+		_, sender1, _ := gomatrixserverlib.SplitID('@', redactedEvent.SenderID())
+		_, sender2, _ := gomatrixserverlib.SplitID('@', redactionEvent.SenderID())
 		var powerlevels *gomatrixserverlib.PowerLevelContent
 		powerlevels, err = plResolver.Resolve(ctx, redactionEvent.EventID())
 		if err != nil {
@@ -1005,7 +999,7 @@ func (d *EventDatabase) MaybeRedactEvent(
 		switch {
 		case powerlevels.UserLevel(redactionEvent.SenderID()) >= powerlevels.Redact:
 			// 1. The power level of the redaction event’s sender is greater than or equal to the redact level.
-		case sender1.Domain() == sender2.Domain():
+		case sender1 == sender2:
 			// 2. The domain of the redaction event’s sender matches that of the original event’s sender.
 		default:
 			ignoreRedaction = true
diff --git a/syncapi/storage/shared/storage_consumer.go b/syncapi/storage/shared/storage_consumer.go
index 3a4758337..2211c257c 100644
--- a/syncapi/storage/shared/storage_consumer.go
+++ b/syncapi/storage/shared/storage_consumer.go
@@ -195,14 +195,7 @@ func (d *Database) StreamEventsToEvents(device *userapi.Device, in []types.Strea
 	for i := 0; i < len(in); i++ {
 		out[i] = in[i].HeaderedEvent
 		if device != nil && in[i].TransactionID != nil {
-			userID, err := in[i].UserID()
-			if err != nil {
-				logrus.WithFields(logrus.Fields{
-					"event_id": out[i].EventID(),
-				}).WithError(err).Warnf("Event has invalid userID")
-				continue
-			}
-			if device.UserID == userID.String() && device.SessionID == in[i].TransactionID.SessionID {
+			if device.UserID == in[i].SenderID() && device.SessionID == in[i].TransactionID.SessionID {
 				err := out[i].SetUnsignedField(
 					"transaction_id", in[i].TransactionID.TransactionID,
 				)
diff --git a/syncapi/streams/stream_invite.go b/syncapi/streams/stream_invite.go
index b35c24fac..2f05382bb 100644
--- a/syncapi/streams/stream_invite.go
+++ b/syncapi/streams/stream_invite.go
@@ -63,11 +63,7 @@ func (p *InviteStreamProvider) IncrementalSync(
 
 	for roomID, inviteEvent := range invites {
 		// skip ignored user events
-		userID, err := inviteEvent.UserID()
-		if err != nil {
-			continue
-		}
-		if _, ok := req.IgnoredUsers.List[userID.String()]; ok {
+		if _, ok := req.IgnoredUsers.List[inviteEvent.SenderID()]; ok {
 			continue
 		}
 		ir := types.NewInviteResponse(inviteEvent)
diff --git a/syncapi/synctypes/clientevent.go b/syncapi/synctypes/clientevent.go
index 2d5daa282..bbd4a75c7 100644
--- a/syncapi/synctypes/clientevent.go
+++ b/syncapi/synctypes/clientevent.go
@@ -57,13 +57,9 @@ func ToClientEvents(serverEvs []gomatrixserverlib.PDU, format ClientEventFormat)
 
 // ToClientEvent converts a single server event to a client event.
 func ToClientEvent(se gomatrixserverlib.PDU, format ClientEventFormat) ClientEvent {
-	sender, err := se.UserID()
-	if err != nil {
-		panic("uh oh! userID does not exist...")
-	}
 	ce := ClientEvent{
 		Content:        spec.RawJSON(se.Content()),
-		Sender:         sender.String(),
+		Sender:         se.SenderID(),
 		Type:           se.Type(),
 		StateKey:       se.StateKey(),
 		Unsigned:       spec.RawJSON(se.Unsigned()),
diff --git a/userapi/consumers/roomserver.go b/userapi/consumers/roomserver.go
index b74f84374..a4cb3defe 100644
--- a/userapi/consumers/roomserver.go
+++ b/userapi/consumers/roomserver.go
@@ -615,11 +615,7 @@ func (s *OutputRoomEventConsumer) notifyLocal(ctx context.Context, event *rstype
 // evaluatePushRules fetches and evaluates the push rules of a local
 // user. Returns actions (including dont_notify).
 func (s *OutputRoomEventConsumer) evaluatePushRules(ctx context.Context, event *rstypes.HeaderedEvent, mem *localMembership, roomSize int) ([]*pushrules.Action, error) {
-	userID, err := event.UserID()
-	if err != nil {
-		return nil, err
-	}
-	if userID.String() == mem.UserID {
+	if event.SenderID() == mem.UserID {
 		// SPEC: Homeservers MUST NOT notify the Push Gateway for
 		// events that the user has sent themselves.
 		return nil, nil