I’ve tried to use a Mailcow mailbox as destination for Exchange 365 journaling (= basically a copy of all 365 mails is send to the Mailcow mailbox, e.g. email@example.com). I’ve listed the 365 sender address (firstname.lastname@example.org) on the spam filter whitelist.
Sadly this works for some mails only. About 30 % can be seen in rspamd. They are accepted and delivered to the mailbox (
The other 70% are not even shown in rspamd, the are rejected beforehand. The 365 admin mailbox shows
Remote Server returned '550 5.1.0 Recipient rejected: email@example.com Not sure why some are rejected and others not.
Maybe it is because the “To:” header shows only non Mailcow domains? Is the To: header checked?
I’ve tried some other mail providers as journal destination and no mails are rejected there.