diff --git a/backup_imap/backup_imap.py b/backup_imap/backup_imap.py
index 4ff5faa..0f546ba 100644
--- a/backup_imap/backup_imap.py
+++ b/backup_imap/backup_imap.py
@@ -149,7 +149,7 @@ class BackupImap:
                             )
                         message_path = os.path.join(
                             mailbox_path,
-                            subject
+                            f"{subject}.eml"
                         )
                         original_subject = subject
                         message_id = self._get_mail_header('Message-ID', data)[-1]