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Exchange 2003 SMTP service causing high latency

A client has an Exchange 2003 server. Usually, pings to the outside world reply in around 30ms but they now take anywhere between 300 - 800ms.

Stop the SMTP service on the server and latency returns to normal. Start it up again and after a few seconds the latency has crept back up agian.

I've enabled detailed logging on the SMTP connector and can see that there's a lot of SMTP activity. In particular, one user is mentioned a lot in reference to sending an email with a 15MB attachement to a yahoo address. I assume this is connected to my problem.

In the queue viewer I can see a couple of queues. One of the queues is for yahoo.com and is active. However, there are no messages in the queue when you open it up and click 'Find Now'.

Bandwidth on the broadband connection actually seems ok and largely unaffected by this. However, ping tests are bad.

My question seems to be this - If there's nothing in the queue, then why is the log file reporting so many communications with the yahoo server?

The 15MB attachment seems the likely culpret but I can't delete the message from the queue because I can't see it!

Any ideas?
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edz_pgt
Asked:
edz_pgt
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1 Solution
 
Alan HardistyCommented:
If you have users sending large attachments to external people and is sending that mail to lots of people, then that is going to eat up your bandwidth and slow everything else down.

You can schedule large emails (over 4mb for example) to be sent out of hours (if you have a quiet period) so that day-to-day stuff doesn't get bogged down by problems such as this, or you can restrict your users from sending large attachments.

If you block TCP Port 25 outbound on your firewall - the message flow should stop and then you can see the messages in the queue and delete the offending ones.  Then open port 25 back up again and problem solved.

When a message is being sent - the queue will appear empty - this is nothing unusual.
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AmitIT ArchitectCommented:
MS recommend to have 10MB attachment size for Exchange 2003. If you can reduce it to 10 MB. That will be first step for stopping this traffic.

Check below article

http://www.msexchange.org/tutorials/Logging_the_SMTP_Service.html

How to monitor it.
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AmitIT ArchitectCommented:
Hi edz_pgt,

You can also try Promodag monitoring tool. It is a paid one, but free for 45 days.

http://www.promodag.com/
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edz_pgtAuthor Commented:
@alanhardisty - What a star! Thankyou thankyou thankyou!

I've been banging my head against a wall with this for days. Such a relief!

One very happy bunny.
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Alan HardistyCommented:
No probs - I'll add guidance on the delaying tactics in a sec!
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Alan HardistyCommented:
If you want send large email messages after hours, please make sure you have an SMTP Connector configured (if not - please set one up following this guide - http://www.msexchange.org/tutorials/Configuring-SMTP-Connector.html, then configure the Connector on the Delivery Options Tab and set the option "Use different delivery times for oversize messages" to enabled and then choose your connection time and size and if you want - customize it with the customize button.

See the image below:
Delivery-Options.png
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edz_pgtAuthor Commented:
Nice one - thanks very much!

Thanks to amitkulshrestha for your input, too.
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AmitIT ArchitectCommented:
@edz_pgt: Thanks for your comments.

One more time great tip from alanhardisty. No doubt why he is on top:)
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Alan HardistyCommented:
On top for now!  Demazter promises to overtake me - but he is not trying hard enough yet (laughing).

Thanks Amit.
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