Thanks for your replies.
No, the address wasn't and has never been valid. But, I didn't add "reject_unlisted_recipient" to "smtpd_recipient_restrictions" in postfix until a couple of days ago. Missed it when it configured the mailserver. Maybe that can have something to say why Astaro thinks this address is valid?
Is there a way to clean out the cache manually?
On other "unknown" addresses that I have tested randomly Astaro dosn't send a bounce message, only to the one address mentioned above.
