check for sender mailer-daemon as link2xt proposed

src/imap/mod.rs

@@ -1458,7 +1458,7 @@ pub(crate) async fn prefetch_should_download(
     let is_reply_to_chat_message = prefetch_is_reply_to_chat_message(context, &headers).await;
 
     let maybe_ndn = if let Some(from) = headers.get_header_value(HeaderDef::From_) {
-        from.to_ascii_lowercase().contains("daemon")
+        from.to_ascii_lowercase().contains("mailer-daemon")
     } else {
         false
     };