diff --git a/app/main.py b/app/main.py
index deb3242..fd3e421 100644
--- a/app/main.py
+++ b/app/main.py
@@ -923,6 +923,10 @@ async def sync_matrix_space() -> dict:
             headers=H)
         invited = {m["state_key"] for m in r.json().get("chunk", [])} if r.status_code == 200 else set()
 
+        # One identity per member: when a member sets a dashboard extra MXID,
+        # their auto-generated local account (@username:inference.coop) should
+        # NOT also sit in the Space. Track the desired set, then retire the
+        # local accounts of members whose dashboard MXID replaced them.
         invited_count = 0
         async for email, mxid in matrix_member_mxids(client):
             if not mxid or mxid in joined or mxid in invited:
@@ -933,6 +937,56 @@ async def sync_matrix_space() -> dict:
             invited_count += 1
         if invited_count:
             logger.info("Matrix space invites sent: %s", invited_count)
+
+        # Retire local accounts: for each member with a dashboard-set external
+        # MXID, kick their @username:inference.coop account if it's currently
+        # in the Space. Only ever touches accounts derived from that member's
+        # own Cloudron username — never other members' or federated accounts.
+        conn = get_db()
+        rows = conn.execute(
+            "SELECT email, matrix_mxid FROM members WHERE active = 1 AND matrix_mxid IS NOT NULL AND matrix_mxid != ''"
+        ).fetchall()
+        conn.close()
+        users: dict[str, str] = {}
+        page = 1
+        async with httpx.AsyncClient(timeout=30) as uc:
+            while True:
+                r = await uc.get(
+                    f"{CLOUDRON_API}/api/v1/users",
+                    params={"page": page},
+                    headers=cloudron_headers(),
+                )
+                if r.status_code != 200:
+                    break
+                batch = r.json().get("users", [])
+                for u in batch:
+                    if u.get("email") and u.get("username"):
+                        users[u["email"].lower()] = u["username"]
+                if len(batch) < 25:
+                    break
+                page += 1
+        retired = 0
+        for email, ext_mxid in rows:
+            username = users.get(email.lower())
+            if not username:
+                continue
+            local_mxid = f"@{username}:inference.coop"
+            if local_mxid == ext_mxid:
+                continue  # dashboard MXID IS the local account — nothing to retire
+            if local_mxid in joined:
+                for room in [MATRIX_SPACE_ID] + ([MATRIX_GENERAL_ROOM] if MATRIX_GENERAL_ROOM else []):
+                    import urllib.parse
+                    enc_room = urllib.parse.quote(room, safe="")
+                    await client.post(
+                        f"{MATRIX_HOMESERVER}/_matrix/client/v3/rooms/{enc_room}/kick",
+                        headers=H,
+                        json={"user_id": local_mxid,
+                              "reason": f"This co-op account is superseded by {ext_mxid} (set on your dashboard)"},
+                    )
+                retired += 1
+                logger.info("Matrix sync: retired local account %s (member uses %s)", local_mxid, ext_mxid)
+        if retired:
+            logger.info("Matrix sync: retired %s local account(s)", retired)
     return {"invited": invited_count}