"SpamAssassin and DSPAM are both open source antispam tools
designed to filter your e-mail and weed out spam. ClamAV is an open
source antivirus package which uses regularly updated signature
files to detect viruses both on your host and in your e-mail. They
are each standalone packages but can be used together if you wish.
Indeed, you will almost certainly need to combine both an antispam
package and an antivirus package. Let's look at each package
"SpamAssassin (SA) is a mail filter written in Perl. It can be
executed via mail processors like procmail or Maildrop, integrated
into your mail server, run against a remote mailbox using IMAP, or
incorporated into a third-party tool like AMaViS..."