Exchange 2003 incoming SMTP network level problem
From: Carol Chisholm (carol.lists_at_smalldomain.ch)
Date: 12/25/04
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Date: Sat, 25 Dec 2004 18:37:32 +0100
This one will probably only be solved with a packet sniffer, but
perhaps someone has already solved this one.
A new Exchange 2003 server does not receive SMTP data from certain
mail hosts when connected to an ADSL connection.
This same server same server receives the SMTP data from all mail
hosts when connected to a cable modem provided by a closely related
ISP.
Now for the gory details.
I built a new exchange server and connected it to a firewall and an
ADSL modem. It did not get mail from some hosts.
First I changed the ADSL modem. (Zyxel 623ME and a 650R). no progress.
Then I changed the firewall (Sonicwall TZ170). No better
Then I built a new Exchange server. No better.
Then I moved the server to another building. Problem solved. (However
the server cannot stay in the other building for ever, I need it back
in it's owner's offices).
It works fine with the cable connection, and erratically with the ADSL
connection.
The "erratic" means:
- some hosts can send mail to it all the time (notably all other
versions of Exchange
- other hosts can't send it mail when sent with software (some Unix
hosts)
- these difficult hosts can however always send it SMTP mail when they
send "manually" with a user typing in telnet x.x.x.x 25, ehlo....
(Of course this slowed the diagnosis greatly because everyone tests
SMTP manually, and it works fine. I have had a hard time getting help
from ISPs because they tell me there is nothing wrong with my server.)
In the Exchange SMTP log I see a connection, and EHLO and then *no*
DATA, BDAT or any kind of data transfer. Eventually there is a
timeout. At the other end the sending host sees a connection, no
refusal, no data transfer and then a timeout.
There are no blacklist and no spam filters.
The two ISPs (cable and ASDL) are related and have very similar
setups.
The firewalls are the same on both sites (Sonicwall TZ170s). I have
swapped the firewall hardware between sites.
The modems are obviously different but both are configured as bridges,
and not doing anything clever. I have tried two different models of
ADSL modem: both Zyxel, a 623ME and a 650R.
The server is the same, a new HP Proliant.
I'm thinking this is related to the version of sendmail the sending
ISPs are using (but no-one will tell me that top secret information)
and to a network level problem somewhere. However it is a rather
daunting task to diagnose, so I'm looking for help.
Happy Christmas.
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