Bounced emails not being detected

It would help a lot if you wrote what you were actually using for settings, even anonymised slightly.

You might also want to look into setting alternative_reply_by_email_addresses.

I don’t believe so.

If possible, for your setup I’d recommend something like:

  • set reply_by_email_address to inbound+%{reply_key}@forum.hostname
  • configure a mail server to receive email for forum.hostname and deliver it all to the.gmail.account@gmail.com

Here the intermediate mail server doesn’t need to understand plus-addressing, it just needs to forward on everything for the domain.