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 {
             to.push(Address::new_group(
                 "hidden-recipients".to_string(),
@@ -541,6 +542,14 @@ impl MimeFactory {
                 }
             }
 
+            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() {
                 to.push(from.clone());
             }
@@ -556,6 +565,9 @@ 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