I posted a query about integrating SpamAssassin with (some mail delivery system), but nobody answered. Should I ask again?

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.

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.