What happens to emails when my E-Mail Server dies?

Hi,

I was just wondering: what does my asg do with incoming emails when my internal E-Mail server suddenly dies.
It's just a hypothetical situation.

Does the smtp proxy have some kind of buffer and it tries to resend the Mails to the server after a while? If yes: for how long does that work?

Or do emails just bounce back in this situation?

Any other helpful information on that matter? I'm trying to get a view on a worst case scenario with my email-server here.

Thanks,
Chris