It appears to me that chudys.com is totally clueless. Their response to your
inquiry is meaningless techno-babble, their mail server is a confirmed open
relay (see below), and their rejection of messages with null return-path
addresses is in violation of Internet mail standards (see RFC 821 and RFC
1123). You did not provide the headers for the rejected message, but the
text of the 550 error message and the null return address on the rejected
message lead me to believe that the return-path address was also null.

--
Paul Russell
Senior Systems Administrator
University of Notre Dame

----- Begin forwarded message -----
>Received: from mail.chudys.com (mail.chudys.com [216.228.97.2]) by
>       dagger.nd.edu (8.10.2/8.10.2) with ESMTP id e9JGOb129235 for
>       <[log in to unmask]>; Thu, 19 Oct 2000 11:24:41 -0500 (EST)
>Received: from sunbear.cc.nd.edu (sunbear.cc.nd.edu [129.74.36.107]) by
>       mail.chudys.com (Postfix) with SMTP id 295B4113005 for
>       <[log in to unmask]>; Thu, 19 Oct 2000 12:23:35 -0400 (EDT)
>Date: 19 Oct 2000 11:23:52 -0500
>Subject: relay test of mail.chudys.com
>To: <[log in to unmask]>
>From: <[log in to unmask]>
>Message-ID: <[log in to unmask]>
>
>This is a test.
----- End forwarded message -----