We receive a a lot of spam addressed to (random) non-existing users. This causes postfix to generate "unknown user" bounces to the fake sender.
As a workaround I use a catch-all to redirect any mail to myself and manually forward mail in cause of typos in the local_part.
I want postfix to drop spams to non-existing users and only bounce them when their spam score is below a threshold. That way people trying to send ham to non-existent users will get a notice and there would be less backscatter.
Here the logs file
Sep 11 07:03:31 srv postfix/smtpd[27382]: connect from mailin.example.com[10.13.185.194]
Sep 11 07:03:31 srv postfix/smtpd[27382]: 563393847D: client=mailin.example.com[10.13.185.194]
Sep 11 07:03:31 srv postfix/cleanup[27386]: 563393847D: message-id=<[email protected]>
Sep 11 07:03:31 srv postfix/qmgr[1771]: 563393847D: from=<[email protected]>, size=5341, nrcpt=1 (queue active)
Sep 11 07:03:31 srv postfix/smtpd[27382]: disconnect from mailin.example.com[10.13.185.194]
Sep 11 07:03:33 srv postfix/pickup[26067]: C53A53851C: uid=115 from=<[email protected]>
Sep 11 07:03:33 srv postfix/cleanup[27386]: C53A53851C: message-id=<[email protected]>
Sep 11 07:03:33 srv postfix/pipe[27387]: 563393847D: to=<[email protected]>, relay=spamassassin, delay=2.5, delays=0.05/0.01/0/2.4, dsn=2.0.0, status=sent (delivered via spamassassin service)
Sep 11 07:03:33 srv postfix/qmgr[1771]: 563393847D: removed
Sep 11 07:03:33 srv postfix/qmgr[1771]: C53A53851C: from=<[email protected]>, size=3784, nrcpt=1 (queue active)
Sep 11 07:03:33 srv postfix/local[27392]: C53A53851C: to=<[email protected]>, relay=local, delay=0.25, delays=0.11/0.01/0/0.13, dsn=5.1.1, status=bounced (unknown user: "kn")
Sep 11 07:03:33 srv postfix/cleanup[27386]: F2879384E6: message-id=<[email protected]>
Sep 11 07:03:34 srv postfix/bounce[27393]: C53A53851C: sender non-delivery notification: F2879384E6
Sep 11 07:03:34 srv postfix/qmgr[1771]: F2879384E6: from=<>, size=5665, nrcpt=1 (queue active)
Sep 11 07:03:34 srv postfix/qmgr[1771]: C53A53851C: removed
Sep 11 07:03:34 srv postfix/smtp[27394]: F2879384E6: to=<[email protected]>, relay=mailout.example.com[10.13.60.4]:25, delay=0.08, delays=0.04/0.01/0.01/0.02, dsn=2.0.0, status=sent (250 OK id=1R2e4j-0001L0-QU)
Sep 11 07:03:34 srv postfix/qmgr[1771]: F2879384E6: removed