let prefetch_should_download() check if it might be an ndn

src/imap/mod.rs

@@ -1449,7 +1449,7 @@ async fn prefetch_is_reply_to_chat_message(
     false
 }
 
-async fn prefetch_should_download(
+pub(crate) async fn prefetch_should_download(
     context: &Context,
     headers: &[mailparse::MailHeader<'_>],
     show_emails: ShowEmails,
@@ -1457,6 +1457,16 @@ async fn prefetch_should_download(
     let is_chat_message = headers.get_header_value(HeaderDef::ChatVersion).is_some();
     let is_reply_to_chat_message = prefetch_is_reply_to_chat_message(context, &headers).await;
 
+    let maybe_ndn = if let Some(subject) = headers.get_header_value(HeaderDef::Subject) {
+        subject.to_ascii_lowercase().contains("fail")
+    } else {
+        false
+    } || if let Some(ctype) = headers.get_header_value(HeaderDef::ContentType) {
+        ctype.starts_with("multipart/report")
+    } else {
+        false
+    };
+
     // Autocrypt Setup Message should be shown even if it is from non-chat client.
     let is_autocrypt_setup_message = headers
         .get_header_value(HeaderDef::AutocryptSetupMessage)
@@ -1467,6 +1477,7 @@ async fn prefetch_should_download(
     let accepted_contact = origin.is_known();
 
     let show = is_autocrypt_setup_message
+        || maybe_ndn
         || match show_emails {
             ShowEmails::Off => is_chat_message || is_reply_to_chat_message,
             ShowEmails::AcceptedContacts => {