diff --git a/crates/colony-cli/src/client.rs b/crates/colony-cli/src/client.rs
index ab64800..5eaf173 100644
--- a/crates/colony-cli/src/client.rs
+++ b/crates/colony-cli/src/client.rs
@@ -90,7 +90,7 @@ impl ColonyClient {
     pub async fn ack_inbox(&self, ids: &[i64]) -> serde_json::Value {
         let body = AckRequest { ids: ids.to_vec() };
         let res = self.http
-            .post(self.url("/api/inbox/ack"))
+            .post(self.url(&format!("/api/inbox/ack?{}", self.config.user_query())))
             .json(&body)
             .send().await.unwrap_or_else(|e| { eprintln!("colony unreachable: {e}"); process::exit(1); });
         if !res.status().is_success() { self.handle_error(res).await; }
diff --git a/crates/colony/src/routes.rs b/crates/colony/src/routes.rs
index 255cb77..422033d 100644
--- a/crates/colony/src/routes.rs
+++ b/crates/colony/src/routes.rs
@@ -392,31 +392,37 @@ pub async fn get_inbox(
 
 pub async fn ack_inbox(
     State(state): State<AppState>,
+    Query(user_param): Query<UserParam>,
     Json(body): Json<AckRequest>,
 ) -> Result<impl IntoResponse> {
+    let user_id = resolve_user(&state.db, &user_param).await?;
+    let mut acked = 0i64;
     for id in &body.ids {
-        sqlx::query("UPDATE inbox SET acked_at = strftime('%Y-%m-%dT%H:%M:%SZ', 'now') WHERE id = ? AND acked_at IS NULL")
+        let result = sqlx::query("UPDATE inbox SET acked_at = strftime('%Y-%m-%dT%H:%M:%SZ', 'now') WHERE id = ? AND user_id = ? AND acked_at IS NULL")
             .bind(id)
+            .bind(&user_id)
             .execute(&state.db)
             .await?;
+        acked += result.rows_affected() as i64;
     }
-    Ok(Json(serde_json::json!({"acked": body.ids.len()})))
+    Ok(Json(serde_json::json!({"acked": acked})))
 }
 
 /// Populate inbox entries when a message is posted
 async fn populate_inbox(db: &SqlitePool, message_id: &str, channel_id: &str, content: &str, sender_id: &str) {
     let mentions = crate::db::parse_mentions(content);
+    let mut notified: std::collections::HashSet<String> = std::collections::HashSet::new();
 
     for mention in &mentions {
         // Resolve mentioned user
-        if let Ok(Some(user_id)) = sqlx::query_scalar::<_, String>("SELECT id FROM users WHERE username = ?")
+        if let Ok(Some(uid)) = sqlx::query_scalar::<_, String>("SELECT id FROM users WHERE username = ?")
             .bind(mention)
             .fetch_optional(db)
             .await
         {
-            if user_id != sender_id {
+            if uid != sender_id && notified.insert(uid.clone()) {
                 let _ = sqlx::query("INSERT INTO inbox (user_id, message_id, channel_id, trigger) VALUES (?, ?, ?, 'mention')")
-                    .bind(&user_id)
+                    .bind(&uid)
                     .bind(message_id)
                     .bind(channel_id)
                     .execute(db)
@@ -432,12 +438,14 @@ async fn populate_inbox(db: &SqlitePool, message_id: &str, channel_id: &str, con
                 .await
                 .unwrap_or_default();
             for agent_id in agents {
-                let _ = sqlx::query("INSERT INTO inbox (user_id, message_id, channel_id, trigger) VALUES (?, ?, ?, 'broadcast')")
-                    .bind(&agent_id)
-                    .bind(message_id)
-                    .bind(channel_id)
-                    .execute(db)
-                    .await;
+                if notified.insert(agent_id.clone()) {
+                    let _ = sqlx::query("INSERT INTO inbox (user_id, message_id, channel_id, trigger) VALUES (?, ?, ?, 'broadcast')")
+                        .bind(&agent_id)
+                        .bind(message_id)
+                        .bind(channel_id)
+                        .execute(db)
+                        .await;
+                }
             }
         }
 
@@ -449,12 +457,14 @@ async fn populate_inbox(db: &SqlitePool, message_id: &str, channel_id: &str, con
                 .await
                 .unwrap_or_default();
             for ape_id in apes {
-                let _ = sqlx::query("INSERT INTO inbox (user_id, message_id, channel_id, trigger) VALUES (?, ?, ?, 'broadcast')")
-                    .bind(&ape_id)
-                    .bind(message_id)
-                    .bind(channel_id)
-                    .execute(db)
-                    .await;
+                if notified.insert(ape_id.clone()) {
+                    let _ = sqlx::query("INSERT INTO inbox (user_id, message_id, channel_id, trigger) VALUES (?, ?, ?, 'broadcast')")
+                        .bind(&ape_id)
+                        .bind(message_id)
+                        .bind(channel_id)
+                        .execute(db)
+                        .await;
+                }
             }
         }
     }