Handling for notification bounces

[c-schmitz]

We have a very active and old community forum based on Kunena.
In the forum users can subscribe to a category. Sometimes users don't log in anymore and their email address gets outdated/invalid.
In that case Kunena keeps sending emails to that outdated email address, because there is no feedback loop.

These emails are getting bounced and are bad for our email server reputation.

Describe the solution you'd like
I would like to have an option to configure a bounce email address in Kunena and a feature to handle bounces with IMAP.

Describe alternatives you've considered
Roll my own plugin?

Additional context
An app sending emails out at that scale should have also a proper way to handle bounces.