I've been reading on this topic since it arose back about two weeks ago and
wish to put in my devalued two cents for what it's worth.  The
 
        501 <@uga.cc.uga.edu:[log in to unmask]>... Unbalanced '<'
 
is very likely a result of the mailer not recognizing the mixed (and valid)
Internet fully qualified domain name in the routed address, but not the
BITNET-style non-domain address.  If so, following RFC 821 (Jonathan B.
Postel's SIMPLE MAIL TRANSFER PROTOCOL document), the mailer is (properly)
looking for a FQDN following the second "@" sign.
 
Following the RFC, the first "@" sign followed by the ":" is the relay host
and everything between ":" and ">" represent the destination user and host
information arguments.  If, for some reason, the machine reporting the 501
failure ("Syntax error in parameters or arguments" officially) is
attempting to handle a VRFY or whatever on the FQDN of the destination, it
isn't going to (and won't) find one since IUBVM.BITNET is not a FQDN.  This
could very well lead to a logically consistent unbalanced "<" since a
recognized FQDN does not appear in the space following the second "@" and
the trailing ">".
 
I've seen this from a few places and it always appears that it is a result
of a mixed FQDN-BITNET mapping in a To: or From: field.  Short of
malconfiguration on some machine, I don't understand why addresses of these
types appear in To: or From: lines (I understand them fully in Return-path:
lines, but not To: or From:, where gateway-types of addressing --
user%host1@host2 -- can be used; possibly someone can enlighten me on these
variations).  At least, that's what I've always attributed these sorts of
501 errors to and my subsequent reading leads to believe that's the central
problem.  Any comments on this theory?
 
Regards,   George
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
George D. Greenwade, Ph.D.                            Bitnet:  BED_GDG@SHSU
Department of Economics and Business Analysis         THEnet: SHSU::BED_GDG
College of Business Administration                    Voice: (409) 294-1266
P. O. Box 2118                                        FAX:   (409) 294-3612
Sam Houston State University              Internet:        [log in to unmask]
Huntsville, TX 77341                      [log in to unmask]
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%