add more details to fallback NDN

if the NDN has no specific error text,
but we know the failed recipient address,
add these information the final message.

src/message.rs

@@ -1533,7 +1533,7 @@ pub async fn handle_mdn(
 pub(crate) async fn handle_ndn(
     context: &Context,
     failed: &FailureReport,
-    error: &str,
+    error: Option<String>,
 ) -> Result<()> {
     if failed.rfc724_mid.is_empty() {
         return Ok(());
@@ -1564,10 +1564,18 @@ pub(crate) async fn handle_ndn(
         )
         .await?;
 
+    let error = if let Some(error) = error {
+        error
+    } else if let Some(failed_recipient) = &failed.failed_recipient {
+        format!("Delivery to {} failed.", failed_recipient).clone()
+    } else {
+        "Delivery to at least one recipient failed.".to_string()
+    };
+
     let mut first = true;
     for msg in msgs.into_iter() {
         let (msg_id, chat_id, chat_type) = msg?;
-        set_msg_failed(context, msg_id, error).await;
+        set_msg_failed(context, msg_id, &error).await;
         if first {
             // Add only one info msg for all failed messages
             ndn_maybe_add_info_msg(context, failed, chat_id, chat_type).await?;

src/mimeparser.rs

@@ -1401,11 +1401,11 @@ impl MimeMessage {
         }
 
         if let Some(failure_report) = &self.failure_report {
-            let error = parts.iter().find(|p| p.typ == Viewtype::Text).map_or_else(
-                || "Non-Delivery-Notification without further details.".to_string(),
-                |p| p.msg.clone(),
-            );
-            if let Err(e) = message::handle_ndn(context, failure_report, &error).await {
+            let error = parts
+                .iter()
+                .find(|p| p.typ == Viewtype::Text)
+                .map(|p| p.msg.clone());
+            if let Err(e) = message::handle_ndn(context, failure_report, error).await {
                 warn!(context, "Could not handle ndn: {}", e);
             }
         }

src/receive_imf.rs

@@ -2647,7 +2647,7 @@ mod tests {
             "shenauithz@testrun.org",
             "Mr.un2NYERi1RM.lbQ5F9q-QyJ@tiscali.it",
             include_bytes!("../test-data/message/tiscali_ndn.eml"),
-            Some("Non-Delivery-Notification without further details."),
+            Some("Delivery to at least one recipient failed."),
         )
         .await;
     }