You can "pull" POP3 mail into a system to process it further.

I'm guessing you're running a Windows system, and most of these are
Unix utilities, but IIRC most have Windows versions out there. My
home setup is to use fetchmail on a cron-job. Every 5 minutes it goes
out, checks my two POP3 servers for new mail, and grabs if present. It
then hands the mail off to Postfix via SMTP for processing and at this
point it behaves just as if you were running your own mail server.
Postfix uses Amavisd-new along with SpamAssasin and ClamAV for
spam/virus filtering.

Messages that fail these tests are quarantined and I never even see
them unless I specifically go and look. Messages that pass are given
to procmail for local delivery and sorting. I then run Dovecot as an
IMAP server so that I can access the mail with any mail program of my
choosing.

This not only affords good spam protection, but I can also check my
email from any computer in the house and pull up the same set of
messages. I also have setup a webmail system (Roundcube) that accesses
the IMAP server, so that I can also check my email remotely just as
easily. You don't have to go quite this elaborate (if I'm not mistaken
fetchmail can hand directly to procmail which can invoke SpamAssasin if
you like), but the tools are out there to help. All of the ones
mentioned here are also free of charge, as well as open source so you
can make changes to the program if you like.

Mike Gaskins