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Exchange 5.5 SMTP mail trouble

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9 replies

by james.golden 2 views

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Setup:
We are running an Exchange 5.5 server sp4 on an IIS server. We have a firewall, which SMTP traffic is fully open on.

Problem: We are getting 400 and 500 series messages to other companies trying to email us. One of two things happens: One, the sending server says there is no response from mail host. But they can resolve our server name, and ping the server. Two, the sending server gets a deferred connection and it still never gets through.

I have tried to isolate what may be causing it for the past 8 WEEKS and have had no success. Most emails get through, but certain places/companies continually don't with the reasons listed above. Any suggestions would be highly appreciated

9 replies

by hstahl

Do you have your inverse DNS records setup correctly? The companies that fail may be because their server attempts a reverse DNS lookup before contacting your server for security reasons.

-Heath

by james.golden

Yea, did check that. Actually I found that it wasn't setup at all. So I had it changed. The situation with that is we have an outside phone company that handles our gateway and firewall. They did miss setting that up. I had that corrected 2 days ago, but we are still having the SMTP problem.

Thanks.

by stephen mynhier

Check your IMS Connector in Exchange Administrator. Look at the Connections tab and see if any Accept Connections restrictions have been set. Look at the Delivery Restrictions tab and see if any have been set.

by james.golden

Yep, that's WIDE open. No Accept Connection restrictions. It is set to accept connections from ANY host. There are also no Delivery Restrictions.

Thanks for the idea. I Appreciate the help.

by john beno

James,

Ok. First, you say they did not do the DNS correctly. Call me stupid, but have you ensured that they have the A record, MX record, and the PTR record for the server? Second, does the firewall subscribe to any form of spam blocker. If so, those companys could be on the list of spam servers and being denign by the firewall. Third, is the IMS configured to use DNS for deliver or Host, and is the TCP/IP settings pointing to the correct DNS server. I would see if I could ping the other company from the Exchange Server. Also, see if they can telnet to your server's IP on port 25 and get a reply from the IMS. Hope these help.

by james.golden

Yep, I quadruple checked. The pointer record was the only thing I could find that was missing. The error message seems to indicate something other than DNS anyway. If they are receiving a 440 error that means their server is contacting ours, but there is a problem somewhere after that.

There is no subscriptions to spam blockers on our firewall. Acutally our firewall is wide open. It allows ALL SMTP traffic.

The IMS is configured to use DNS,and the TCP/IP settings are correct. I can ping their server, they can ping ours, and resolve our name. And they were able to telnet to port 25.

Thanks for all the things to check for I appreciate it. I'm wondering if maybe the hardware can't handle it or something? It doesn't make sense to me, we only have about 700 users on our exchange server. Is it maybe I'll have to split the traffic to handle the mail load? When I watch on performance monitor I never seem to catch a huge amount of SMTP traffic. hmmmm....

by cscript

I will wade into this one, with a guess.
IMS servers can only handle so many connections at a time. This includes outgoing connections. Check your queues. Do you have a lot of <> originators (sort on orginiator)? If so, those are NDR's being sent to various places and each one takes up a connection as it retries. Since the domain is unreachable it will take some time to time-out. (this is usually caused by spammers spoofing their addresses.) Just because you can ping the server, does not meanthat the server is able to talk on port 25 with any speed. I would suggest doing it manually once or twice from the outside and see what happens. Even if what I stated above is not the case, a manual SMTP send will open your eyes a lot of times to the problem. But if you have a domain that is spammed a lot, the IMS's don't handle it well. If my company did not use SMTP gateways, my 3 IMS's would keel over and die from spammers. (and I would get the same indications that you are getting)

Regards, Good Luck!

by james.golden

Sorry, I forgot to come back and answer this question. I actually did try some of these, but couldn't really come to any concrete conclusions. So I made a best guess which is what you were suggesting about not handling the connections. I stuck ina IIS SMTP gateway, built a new exchange server behind it. That seemed to resolve the problem. Thanks everyone, I really appreciate the suggestions and help.

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