Send Chat-Group-Past-Members header

Author: link2xt

src/mimefactory.rs

@@ -510,6 +510,7 @@ impl MimeFactory {
         };
 
         let mut to = Vec::new();
+        let mut past_members = Vec::new(); // Contents of `Chat-Group-Past-Members` header.
         if !undisclosed_recipients {
             let email_to_remove = match &self.loaded {
                 Loaded::Message { msg, .. } => {
@@ -535,6 +536,14 @@ impl MimeFactory {
                     to.push(new_address_with_name(name, addr.clone()));
                 }
             }
+
+            for (name, addr) in &self.past_members {
+                if name.is_empty() {
+                    past_members.push(Address::new_mailbox(addr.clone()));
+                } else {
+                    past_members.push(new_address_with_name(name, addr.clone()));
+                }
+            }
         }
 
         if to.is_empty() {
@@ -554,6 +563,11 @@ impl MimeFactory {
             headers.push(Header::new_with_value("Sender".into(), vec![sender]).unwrap());
         }
         headers.push(Header::new_with_value("To".into(), to.clone()).unwrap());
+        if !past_members.is_empty() {
+            headers.push(
+                Header::new_with_value("Chat-Group-Past-Members".into(), to.clone()).unwrap(),
+            );
+        }
 
         let subject_str = self.subject_str(context).await?;
         let encoded_subject = if subject_str