I have a Postfix server that receives mail for virtual aliases and forwards them to the real destination addresses. When the final mail server returns an error the bounce message returned to the sender reveals the final destination email address. Eg. if my server receives mail for email@example.com and tries unsuccessfully to send it to firstname.lastname@example.org the bounce message looks something like this:
I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below. For further assistance, please send mail to postmaster. If you do so, please include this problem report. You can delete your own text from the attached returned message. The mail system <email@example.com> (expanded from <firstname.lastname@example.org>): host final.mail.host.com said: 553 5.1.8 <email@example.com>... <some error> (in reply to RCPT TO command)
How do I stop it from revealing the final address?