EMail bouncing: needs more details about how to configure it


While waiting for re-enabling this plugin (see post, I was trying to better understand some settings.

One that puzzle me is the bouncing settings.

I think I'm missing some knowledge of how it works and I need some more details.

I send newsletter with the address new@something.tld

If an email is bounced, I suppose it will be sent to the same address.
Instead, e-Newsletter ask me for a different email address: why?

How could the bounced message goes there?

In a nutshell, how does the bounced message/handling works?