Hi Rafael,
quick thoughts. Do you have smtpd_recipient_restrictions = reject_unauth_destination in your main.cf? The request should be rejected and not be queued. Greets, Ludi Von: owner-postfix-us...@postfix.org <owner-postfix-us...@postfix.org> Im Auftrag von Rafael Azevedo Gesendet: Dienstag, 29. Dezember 2020 13:38 An: Postfix users <postfix-users@postfix.org> Betreff: SPAM attack from bounce techniques Hi there, I've noticed that one of our servers is receiving a huge amount of unauthorized requests. User connects to our server and tries to send an email to any destination. Our servers denies the message because user is not authenticated. Then, a bounce is generated to the source address, which was fake and turns to be the final destination, so at the end, the email is actually sent as a bounce, proliferating lots of spam. Is there a way to avoid this? Thanks in advance. BR, Rafael
