Sendmail weirdness

[dkatz at kenan.com (Daniel P. Katz)]

Hi.

	I have a RH 6.0 box attached to a LAN, and I have found an unusual mail
issue:  the mail goes out but it doesn't come in!  I can send mail to
any other machine on the network, but when any other machine tries to
send mail to me, it bounces.  After a little digging, I found the
"verbose switch" in /bin/mail which yielded the following "sendmail
conversation" between bishop (a Solarix box on the LAN) and cam-katz
(the linux box in question):

-------------------------------------------------------------------------
bishop:/users/dkatz[1]% mail -v dkatz at cam-katz
Subject: verbosity test
This is also a verbosity test.
EOT
bishop:/users/dkatz[2]% dkatz at cam-katz... Connecting to
dhcp-250-11.kenan.com. via esmtp...
220 cam-katz.kenan.com ESMTP Sendmail 8.9.3/8.9.3; Fri, 15 Oct 1999
16:01:58 -0400
>>> EHLO bishop.kenan.COM
250-cam-katz.kenan.com Hello bishop.kenan.com [198.187.250.57], pleased
to meet you
250-EXPN
250-VERB
250-8BITMIME
250-SIZE
250-DSN
250-ONEX
250-ETRN
250-XUSR
250 HELP
>>> MAIL From:<dkatz at bishop.kenan.COM> SIZE=94
250 <dkatz at bishop.kenan.COM>... Sender ok
>>> RCPT To:<dkatz at dhcp-250-11.kenan.com>
550 <dkatz at dhcp-250-11.kenan.com>... Relaying denied
dkatz at cam-katz... User unknown
>>> RSET
250 Reset state
----------------------------------------------------------------------------

I assure you that dkatz is a valid user on cam-katz, so the questions
are:

a) How does sendmail decide if a user is "known" or not?
b) Is this an intentional security feature or a configuration error?
c) Has anyone else seen this and do you know how to fix it.

While I don't mind reading documentation, the Sendmail book is a bit
long to read casually.  I'm hoping you can help me avoid that fate. 
Thanx.

Dan Katz
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