zmailer smtp delivery problem

[James S MacKinnon <jmack@phys.ualberta.ca>]

Hi,

        I've got a curious situation with zmailer and a SUN host(ecad1)
who refuses to acknowledge requests from the deliverer(tshimshan) that
a message is to be accepted. The smtp logfile shows a repetitive sequence
which eventually stops when the message expires:

...
11641#  smtpopen: connecting to ecad1.phys.ualberta.ca
11641#  smtpconn: host = ecad1.phys.ualberta.ca
11641#  smtpconn: retval = 75
11675#  smtpopen: connecting to ecad1.phys.ualberta.ca
11675#  smtpconn: host = ecad1.phys.ualberta.ca
11675#  smtpconn: retval = 75
...

The mailq shows:

0 entries in router queue: idle
0 entries in scheduler queue: scheduling transports
2 messages in transport queue
smtp/ecad1.phys.ualberta.ca:
        5914:   (retry in 18m3s, expires in 2d13h)
          id    <9211180714.AA00267@ecad1.phys.ualberta.ca>
          from  <@stoney.phys.ualberta.ca:jmack@ecad1.phys.ualberta.ca>
          to    jmack@ecad1.phys.ualberta.ca
        5913:   (retry in 18m3s, expires in 2d7h)
          id    <92Nov17.183305mst.5913@phys.ualberta.ca>
          from  James S MacKinnon <jmack>
          to    jmack@ecad1.phys.ualberta.ca

ecad1 is a SUN running SUNOS 4.1 and tshimshan is a NeXT running Mach2.2.
Zmailer is running on tshimshan, and ecad1's MX record points to tshimshan.
I can 'fake' sending a message to ecad1 on port 25 manually, and this is
accepted and delivered.

It looks like there is some sort of handshake failure between them, but so
far, I've been unable to determine the problem. I've got debugging turned
on, and for other hosts, the smtp transaction is quite verbose. But here it
never gets started at all for ecad1.

I'd appreciate any comments or further suggestions as to how to proceed.

Thanks,
-- 
James S. MacKinnon             Office: P-139 Avahd-Bhatia Physics Lab
Center for Subatomic Research  Phone : (403) 492-8226
Department of Physics          email : jmack@phys.ualberta.ca
University of Alberta          uucp  : uofaphys!jmack  iskye!jmack
Edmonton, Canada T6G 2N5       bitnet: jmack@triumfcl  jsm1@ualtamts