Do not count mailinglist contacts as 'known'.

src/chat.rs

@@ -1105,7 +1105,11 @@ pub fn create_by_msg_id(context: &Context, msg_id: MsgId) -> Result<ChatId, Erro
             msg_id: MsgId::new(0),
         });
     }
-    Contact::scaleup_origin_by_id(context, msg.from_id, Origin::CreateChat);
+
+    // If the message is from a mailing list, the contacts are not counted as "known"
+    if !chat.is_mailing_list() {
+        Contact::scaleup_origin_by_id(context, msg.from_id, Origin::CreateChat);
+    }
     Ok(chat.id)
 }
 
@@ -2526,7 +2530,6 @@ pub(crate) fn get_chat_id_by_mailinglistid(
     )
 }
 
-
 /// Adds a message to device chat.
 ///
 /// Optional `label` can be provided to ensure that message is added only once.

src/dc_receive_imf.rs

@@ -1785,19 +1785,22 @@ mod tests {
 
         let chats = Chatlist::try_load(&t.ctx, 0, None, None).unwrap();
         assert_eq!(chats.len(), 1);
+
         let chat_id = chat::create_by_msg_id(&t.ctx, chats.get_msg_id(0).unwrap()).unwrap();
         let chat = chat::Chat::load_from_db(&t.ctx, chat_id).unwrap();
+
         assert!(chat.is_mailing_list());
         assert_eq!(chat.can_send(), false);
         assert_eq!(chat.name, "deltachat/deltachat-core-rust");
         assert_eq!(chat::get_chat_contacts(&t.ctx, chat_id).len(), 0);
 
-
+        
         dc_receive_imf(&t.ctx, MAILINGLIST2, "INBOX", 1, false).unwrap();
 
         let chats = Chatlist::try_load(&t.ctx, 0, None, None).unwrap();
         assert_eq!(chats.len(), 1);
-        assert!(Contact::get_all(&t.ctx, 0, None as Option<String>).unwrap().is_empty());
+        let contacts = Contact::get_all(&t.ctx, 0, None as Option<String>).unwrap();
+        assert_eq!(contacts.len(), 0); // mailing list recipients and senders do not count as "known contacts"
     }
 
     #[test]

src/param.rs

@@ -118,7 +118,7 @@ pub enum Param {
     /// For MDN-sending job
     MsgId = b'I',
 
-    MailingList = b't'
+    MailingList = b't',
 }
 
 /// Possible values for `Param::ForcePlaintext`.