I found some info but haven't tried it...

First I seached sysop.gui for headers... you see how to save headers for nntp
(news) messages and email messages.

Then I loaded sysop.txt into the joe editor, an editor I use.   I found this
with a search for headers in that file:

=========================
702      Global: FidoNet: BOGUS: Log headers(BMT)
Global: FidoNet: BOGUS: Log headers(BMT)
_______________________________________________________________________________

If this option is enabled, BMT will log info about messages passing your
system.
==========================

Sounds like it's what you are looking for but I can't try it right now.. It
could be for email again?  Not sure.

Take care,
Janis

--- BBBS/Li6 v4.10 Dada-2