Sendmail miscommunication (3.5 -> 4.1)

[Chris Andersen The Dangerous Guy]

We've recently begun looking into upgrading our systems from SunOS 3.5 to
4.1.  As part of this work I set up an evaluation copy of 4.1 on one of
our nodes and began working on producing a stable environment for our
development.  While doing this, I noticed an "interesting" problem in
communication between sendmail running on the server (running 3.5) and my
node running 4.1.

If I go on the server and try to mail to 'user at node', sendmail routes the
message to the sendmail daemon on the 4.1 node with the address
'user at node.uucp'.  The 4.1 node correctly sends the message to 'user'.
However, if I tell the server to send to 'node!user', the server's
sendmail translates the address to 'user at node.server.uucp' and sends it to
the node's sendmail daemon for further processing (like before).  The
node's sendmail attempts to parse this address but can't figure it out, so
it re-routes it BACK to the server to see if it can figure it out.  The
server, of course, repeats what it just did and sends it back to the node.
The node repeats what it did and sends it back to the server...and so on
until the message bounces due to an 'alias loop'.

Does anyone have any idea what might be causing this problem?

Chris Andersen (..!uunet!sequent!toontown!chris)