incoming mail ends up in badmail folder

[itgraff]

hi everyone,
I'd be thankful for some help. Using Exchange Server 2000
sp3 and gfi mail essentials 8, I find that some (not all)
incoming mail is not being distributed but ends up in the
badmail folder.
The corresponding *.bdr files always read 'error is
processing file in pickup directory', no other error code
or number is visible.
The mails in question do have valid 'from:' and 'to:'
addresses.

Since all I found on this topic is with regard to using
cdonts and therefore (presumeably) not applicable in this
case, this is beyond me.

Since I am quite new to this whole business, please bear
with me if I forgot to include necessary information and
just let me know. I'll try to post everything that's
needed.

Thanks for helping!