Try e-mailing with an ARPA % hack notation e.g.,
 
to: [log in to unmask]
 
If you get a similar "bounce," then I would assume that their is
a problem in the SMTP protocol used between home.ease.lsoft.com
and igc.apc.org.
 
If you do not get a bounce, I would start considering the BANG
(!) that is part of your listname which looks more like an e-mail
syntactic element than a character of a userid which might
confuse the receiving (igc) system.
 
/Pete Weiss at Penn State