I'm having lots of spam mail to mailman-bounces. I installed spamasssassin and read about sa-learn command.

But I need to set the spam mail apart from others, don't I. I just don't know what to do these mails.

What do you do for these request? There are options like "Preserve messages for the site administrator" and "Forward messages". And what to do " Defer, Accept, Reject, Discard "?