Trying to send external mail to a local sendmail box

[nsyte]

I need some help. I am running sendmail on a local machine
(ion.somedomain.com) separated by a packet filtering firewall
(gateway.somedomain.com), and I have an external DNS (authoritative for
somedomain.com). The DNS MX records point to gateway; gateway forwards
all port 25 traffic to ion.

Because the mail servers of the world will not accept mail from a non-
existent host, I set up the external DNS records to alias ion to
gateway. Now I can successfully send mail out.

I can telnet to port 25 of ion and manually construct a mail session;
however, when I address mail from an external client to
user at somedomain.com or user at ion.somedomain.com, I get the messages
below.

It does not appear that the mail is getting past gateway. Do I have the
DNS set up correctly? I cannot point the MX records to anything besides
gateway. It should forward mail traffic to ion, right?

Where is the problem?

Thanks for your help.


---------------------------------------------------------------
(to user at ion.somedoman.com)

The original message was received at Sun, 12 Mar 2000 01:29:46 -0600
(CST)from ccis01.baylor.edu [129.62.1.18]

   ----- The following addresses had transient non-fatal errors -----
<user at gateway.somedomain.com>

   ----- Transcript of session follows -----
<user at gateway.somedomain.com>... Deferred: Connection timed out with
gateway.somedomain.com.
Warning: message still undelivered after 4 hours

----------------------------------------------------------------------
(to user at somedomain.com)

The original message was received at Sat, 11 Mar 2000 14:26:50 -0600
(CST) from ccis01.baylor.edu [129.62.1.18]

   ----- The following addresses had transient non-fatal errors -----
<user at somedomain.com>

   ----- Transcript of session follows -----
<user at somedomain.com>... Deferred: Connection timed out with
gateway.somedomain.com.
Warning: message still undelivered after 4 hours
Will keep trying until message is 5 days old



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