diff --git a/backup_imap/backup_imap.py b/backup_imap/backup_imap.py
index 24df7da..354b45c 100644
--- a/backup_imap/backup_imap.py
+++ b/backup_imap/backup_imap.py
@@ -131,7 +131,7 @@ class BackupImap:
                     data = fetch_data[0][1]
                     subjects = self._get_mail_header('Subject', data)
                     if len(subjects) > 0:
-                        subject = subjects[-1]
+                        subject = subjects[-1].replace(os.path.sep, '_').replace('\r', '_').replace('\n', '_').replace(':', '_')
                     message_path = os.path.join(
                         mailbox_path,
                         subject