[Mimedefang] Error bouncing mail

[Fox, Randy]

I'm intermittently seeing the following sequence in my maillog:

Sep 24 15:19:44 server1 sendmail[23558]: h8OKJdV5023558: from=<ckoa at colin-okashimo.com.sg>, size=12287, class=0, nrcpts=1, msgid=<00a401c36abe$9f64f4f0$40fa64c0 at pearl>, proto=ESMTP, daemon=MTA, relay=bb-203-125-104-185.singnet.com.sg [203.125.104.185]
Sep 24 15:19:45 server1 mimedefang[23560]: h8OKJdV5023558: Bouncing because filter instructed us to
Sep 24 15:19:45 server1 sendmail[23558]: h8OKJdV5023558: Milter: data, reject=554 5.7.1 Command rejected
Sep 24 15:19:45 server1 sendmail[23558]: h8OKJdV5023558: to=<valid-internal-address at csgsystems.com>, delay=00:00:02, pri=42287, stat=Command rejected

I have gone through my filter (using version 2.34) and every instance of calling action_bounce also includes text as to why the bounce.  I also use filter_recipient and filter_sender but they also return text suggesting why the reject.

Where can I look to see what else could be interpreted as the filter telling sendmail/mimedefang to reject mail?

Thanks,
Randy