diff --git a/src/receive_imf.rs b/src/receive_imf.rs
index e1f7ce283..6f84de655 100644
--- a/src/receive_imf.rs
+++ b/src/receive_imf.rs
@@ -769,6 +769,18 @@ async fn add_parts(
             info!(context, "Message is an MDN (TRASH).",);
         }
 
+        // Try to assign to a chat based on Chat-Group-ID.
+        if chat_id.is_none() {
+            if let Some(grpid) = mime_parser.get_chat_group_id() {
+                if let Some((id, _protected, blocked)) =
+                    chat::get_chat_id_by_grpid(context, grpid).await?
+                {
+                    chat_id = Some(id);
+                    chat_id_blocked = blocked;
+                }
+            }
+        }
+
         if chat_id.is_none() {
             // try to assign to a chat based on In-Reply-To/References:
 
@@ -1035,6 +1047,18 @@ async fn add_parts(
             chat_id = Some(DC_CHAT_ID_TRASH);
         }
 
+        // Try to assign to a chat based on Chat-Group-ID.
+        if chat_id.is_none() {
+            if let Some(grpid) = mime_parser.get_chat_group_id() {
+                if let Some((id, _protected, blocked)) =
+                    chat::get_chat_id_by_grpid(context, grpid).await?
+                {
+                    chat_id = Some(id);
+                    chat_id_blocked = blocked;
+                }
+            }
+        }
+
         if chat_id.is_none() {
             // try to assign to a chat based on In-Reply-To/References:
 
diff --git a/src/receive_imf/tests.rs b/src/receive_imf/tests.rs
index 8e16a29cd..216a7ed94 100644
--- a/src/receive_imf/tests.rs
+++ b/src/receive_imf/tests.rs
@@ -2693,6 +2693,103 @@ Second thread."#;
     Ok(())
 }
 
+/// Test that `Chat-Group-ID` is preferred over `In-Reply-To` and `References`.
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_chat_assignment_chat_group_id_preference() -> Result<()> {
+    let t = &TestContext::new_alice().await;
+
+    receive_imf(
+        t,
+        br#"Subject: Hello
+Chat-Group-ID: eJ_llQIXf0K
+Chat-Group-Name: Group name
+Chat-Version: 1.0
+Message-ID: <first@localhost>
+References: <first@localhost>
+Date: Fri, 28 May 2021 10:15:05 +0000
+From: Alice <alice@example.org>
+To: Bob <bob@example.com>, <claire@example.org>
+Content-Type: text/plain; charset=utf-8; format=flowed; delsp=no
+Content-Transfer-Encoding: quoted-printable
+
+Hello, I've just created a group for us."#,
+        false,
+    )
+    .await?;
+    let group_msg = t.get_last_msg().await;
+
+    receive_imf(
+        t,
+        br#"Subject: Hello
+Chat-Version: 1.0
+Message-ID: <second@localhost>
+References: <second@localhost>
+Date: Fri, 28 May 2021 10:15:05 +0000
+From: Bob <bob@example.com>
+To: Alice <alice@example.org>
+Content-Type: text/plain; charset=utf-8; format=flowed; delsp=no
+Content-Transfer-Encoding: quoted-printable
+
+Hello from Bob in 1:1 chat."#,
+        false,
+    )
+    .await?;
+
+    // References and In-Reply-To point to a message
+    // already assigned to 1:1 chat, but Chat-Group-ID is
+    // a stronger signal to assign message to a group.
+    receive_imf(
+        t,
+        br#"Subject: Hello
+Chat-Group-ID: eJ_llQIXf0K
+Chat-Group-Name: Group name
+Chat-Version: 1.0
+Message-ID: <third@localhost>
+In-Reply-To: <second@localhost>
+References: <second@localhost>
+Date: Fri, 28 May 2021 10:15:05 +0000
+From: Bob <bob@example.com>
+To: Alice <alice@example.org>, <claire@example.org>
+Content-Type: text/plain; charset=utf-8; format=flowed; delsp=no
+Content-Transfer-Encoding: quoted-printable
+
+Hello from Bob in a group."#,
+        false,
+    )
+    .await?;
+
+    let msg = t.get_last_msg().await;
+    assert_eq!(msg.text, "Hello from Bob in a group.");
+    assert_eq!(msg.chat_id, group_msg.chat_id);
+
+    // Test outgoing message as well.
+    receive_imf(
+        t,
+        br#"Subject: Hello
+Chat-Group-ID: eJ_llQIXf0K
+Chat-Group-Name: Group name
+Chat-Version: 1.0
+Message-ID: <fourth@localhost>
+In-Reply-To: <second@localhost>
+References: <second@localhost>
+Date: Fri, 28 May 2021 10:15:05 +0000
+From: Alice <alice@example.org>
+To: Bob <bob@example.com>, <claire@example.org>
+Content-Type: text/plain; charset=utf-8; format=flowed; delsp=no
+Content-Transfer-Encoding: quoted-printable
+
+Hello from Alice in a group."#,
+        false,
+    )
+    .await?;
+
+    let msg_outgoing = t.get_last_msg().await;
+    assert_eq!(msg_outgoing.text, "Hello from Alice in a group.");
+    assert_eq!(msg_outgoing.chat_id, group_msg.chat_id);
+
+    Ok(())
+}
+
 /// Test that read receipts don't create chats.
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn test_read_receipts_dont_create_chats() -> Result<()> {