I don't know off hand if it is the same site, but there is one host in
South Dakota that always bounces, and has for many months, my replys
to lists that have wrapped Reply-To: lines.  If I edit the lines so
they don't wrap, the reply goes through.  If I forget and leave them
as they are, they bounce.  The error message usually says "user unknown".
 
Douglas Winship
Austin, Texas
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