[Mimedefang] suspicious characters in headers

[Fred Bacon]

Lately, I've been having problems with legitimate messages being
quarantined due to "suspicious characters in headers".  The messages in
question come from a Government mailing list from the National Institute
of Allergy and Infectious Diseases.  I can't see anything which I would
consider suspicious in the headers listed in the quarantine message.

Could someone explain what constitutes "suspicious characters" and how
this might be circumvented for these messages?  Is there any control
over the algorithm, or is this a case where I have to turn off this
feature completely to avoid the problem?

I'm running mimedefang 2.68 on a fully patched CentOS 5 system.

Fred Bacon