Outbound e-mail issue - HELP!!

[TweakMYbox]

This Attorney at my firm is constantly complaining about e-mail delays to a particular client. Typically takes 3 to 4 hours for the client to recieve the messages.

Looking at the queues on our outbound Exchange Server, I verified that the messages build up, and every 2 hours or so, a few of them will leave the queue, and reach the recipient.

We are not experiencing a similar issue with any other domain. I contacted the parent company that hosts the DNS, and SMTP servers for the problematic domain. I was able to successfully send a message to the parent company's domain with no problems. The parent domain has the same MX records as the domain in question.

My SMTP logs don't really tell me much. They claim that we are the only domain they are experiencing delays with. I am able to telnet to their SMTP servers and send messages from our Outbound server.. flushed DNS, cleared DNS Cache from all of the internal / external DNS Servers. Message Tracking center simply shows that the messages are queued for delivery.

I'm lost!! If anyone can help me uncover this issue, I will be forever in your debt! HELP! PLEASE!

Mike Fegan, MCSE

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[ShackDaddy]

When you go to DNSStuff.com and put their domain in the 'email' box and do an analysis, what do you get? It would be easiest for us to help if we knew what the destination domain was.

Initially this sounds like some sort of tarpitting process happening on the remote mailserver to dissuade spammers. It could be that they accept most senders without tarpitting, but if other characteristics of your sending server merit it, tarpitting is in place for your messages. And it could be that other people whose mail is affected by this domain's tarpitting just aren't complaining about it.

Tarpitting is when the destination mail server delays accepting the mail for a period of time. This interval could be minutes or hours. Spammers usually won't wait to resubmit, so the spam never gets delivered, but valid servers will patiently wait for the period of time that the remote server requested, and then reattempt delivery (usually successfully).

More on tarpitting:

http://en.wikipedia.org/wiki/Tarpit_(networking)

Look into Greylisting too, which is the practice some SMTP servers have of rejecting the first attempt of an unknown mail server to connect to them and then allowing subsequent connections. But I would expect a remote greylisting to empty your queue all at once and not introduce significant delays.

ShackDaddy
Shackelford Consulting

 

[TweakMYbox]

Good info! Thanks. The domain name is colfin.com.... DNS shows that they have duplicate MX records, and a few other issues - but nothing that I would think would cause these significant delays.