The
SpamAssassin build is fairly straightforward. We use SpamAssassin as a filter in procmail:
:0fw : spamassassin.lock
* < 256000
| spamassassin:0
* ^X-Spam-Flag: YES
{
CHALLENGE=1
}(The "CHALLENGE=1" assignment is picked up by TMDA, which is further down the procmail chain.)