We've been trying to make bounce handling work but with no success so far.
The fact is that it used to work setting a gmail.com email address as in this forum thread (see below), but all of a sudden it stopped working and it has nothing to do with opening port 993, because it was already open.
Server imap.gmail.com Username email@example.com Password (triple checked against gmail account) Localpart xxx+ Email Domain gmail.com Return-Path (empty) Protocol IMAP Source (empty) Use SSL? Y Used For? Bounce Processing
When sending a test mail to wrong email accounts CiviMail counts them as correct addresses.
Thank you very much for you help