Chances are, we don't know the answer; the SpamAssassin developers concentrate on making the core SpamAssassin code work well, not on integrating it with other mail platforms. You may get a better answer by asking your query in a forum dedicated to the mail system you're using.
If {{spamassassin -tD < \[message_file\]}} returns a properly filtered message, then [SpamAssassin] is working appropriately. You should check with the folks who support your MTA filter (MIMEdefang, qmail-scanner, spampd, etc) for support. The best messages to use for this test are the samples included with the distribution, \[http://spamassassin.org/full/3.0.x/dist/sample-spam.txt sample-spam.txt\] and \[http://spamassassin.org/full/3.0.x/dist/sample-nonspam.txt sample-nonspam.txt\]. |
If you manage to solve the problem on your own, however, please do mail the spamassassin-talk list and explain what your problem was and how you fixed it so that people with your problem in the future will be able to find the answer.