diff --git a/src/mimefactory.rs b/src/mimefactory.rs
index cd9ddc6bc2..8dd7d7850b 100644
--- a/src/mimefactory.rs
+++ b/src/mimefactory.rs
@@ -543,6 +543,11 @@ impl MimeFactory {
             for (name, addr) in &self.recipients {
                 if let Some(email_to_remove) = email_to_remove {
                     if email_to_remove == addr {
+                        if name.is_empty() {
+                            past_members.push(Address::new_mailbox(addr.clone()));
+                        } else {
+                            past_members.push(new_address_with_name(name, addr.clone()));
+                        }
                         continue;
                     }
                 }
@@ -563,6 +568,11 @@ impl MimeFactory {
             }
         }
 
+        debug_assert!(
+            undisclosed_recipients
+                || self.member_timestamps.is_empty()
+                || to.len() + past_members.len() == self.member_timestamps.len()
+        );
         if to.is_empty() {
             to.push(Address::new_group(
                 "hidden-recipients".to_string(),