Fetchmai & postfix reject

Hi,

i'm running a dialup-server with fetchmail & postfix.
If postfix is rejecting some strange mail by header or body check, where
does the mail left ?

By default fetchmail gets all mail from my provider, if postfix reject
the mail it is rejected to whom ?
What happens with this mail ?

It's just a question of Knowledge, but i have no clue about it.

Can someone enlight me ?

Stefan