In amavisd.conf you'll have a few options that can be useful.
The options are :
$final_X_destiny if you set it to D_BOUNCE, amavisd will create a DSN to the sender, this can be problematic if you're being spammed with spoofed addresses, you might want to look into creating a policy bank for authenticated users, and using this option just there.
The other option you have is the
$X_quarantine_to if you set that to a particular email, you could run a script that checks the mailbox, and sends messages to people..
This page has some further info also, including the spam counterparts to these options.