Blocked BAD-HEADER-0 {RejectedInbound,Quarantined

I've got a few remote senders whose messages my server is rejecting and 
putting this in syslog: Blocked BAD-HEADER-0 {RejectedInbound,Quarantined

I've got this in my amavis configuration, so I believe that this is the 
expected behavior:

$final_bad_header_destiny = D_REJECT;

How do I determine what exactly is wrong with the header that the remote 
server is sending?  These messages are originating from another 
organization (very large company) and it's going to be a challenge to 
get them to fix their systems even if I can prove exactly what they are 
doing wrong.

If I can't get the remote site to fix their stuff, is there a way to 
bypass the header check for their domains only?

-- 
Todd D. Taft
[email protected]