[Mimedefang] Mimedefang dropping mail discard with no reason in log file - mail relay from hostname.roaringpenguin.com

[Jon Rowlan]

I have a curious problem that email from a domain to a domain hosted by
us is being discarded with no reason given.

Their email when relayed via a separate relay server, which it looks
like protected by CanIt, comes through ok, its only the one relay server
that seems to be met with discard.

The gist of the messages in my log are:

Mar  5 16:36:15 ant sm-mta[3694]: t25GaFwa003694: Milter (mimedefang):
init success to negotiate
Mar  5 16:36:15 ant sm-mta[3694]: t25GaFwa003694: Milter: connect to
filters
Mar  5 16:36:15 ant sm-mta[3694]: t25GaFwa003694: milter=mimedefang,
action=connect, continue
Mar  5 16:36:16 ant sm-mta[3694]: t25GaFwa003694: milter=mimedefang,
action=helo, continue
Mar  5 16:36:16 ant sm-mta[3694]: t25GaFwa003694: milter=mimedefang,
action=mail, continue
Mar  5 16:36:16 ant sm-mta[3694]: t25GaFwa003694: ruleset=check_rcpt,
............ relay=hostname.roaringpenguin.com [x.x.x.x], discard
Mar  5 16:36:17 ant sm-mta[3694]: t25GaFwa003694: Milter (mimedefang):
abort filter
Mar  5 16:36:17 ant sm-mta[3694]: t25GaFwa003694: Milter accept: message
Mar  5 16:36:17 ant sm-mta[3694]: t25GaFwa003694: discarded

I think I should get a little more detail than this should I not?

Does anyone have any thoughts? 

Does MD not like receiving from other MD servers .... have they had a
falling out or just not talking to each other :-)

jON