Re: Exchange 2003 incoming SMTP network level problem
From: Olivier (ok_at_ok.ch)
Date: 12/27/04
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Date: Mon, 27 Dec 2004 01:21:43 +0100
Carol Chisholm a écrit :
> 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.
Hey,
Maybe try to modifiy the MTU site of your IP Stack
It can be done with a tool called drtcp.exe (Google)
Select your adapter then modifiy the MTU (Default is 1500, put 1400 and
save)
Restart the server and try again (Run drtcp.exe to be sure that your
new value are still there)
Happy New Year from Switzerland
Olivier
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- Next message: Keith 'StarPilot' Barrows: "Re: Exch Server refuses connection"
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