Mail is rejected with error message:
CMR-HDR-OE-EOL
Cleanmail no longer accepts messages created by Microsoft Outlook Express. Microsoft ended support in 2009 and replaced it by Windows Mail
This software has not received any security updates for more than 9 years, its use is strongly discouraged.
Nowadays Outlook Express, resp. headers which claim creation by Outlook Express, are almost exclusively used by spammers.