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Exchange 2000 reverse DNS

By Jellimonsta ·
I originally posted this in discussions as I fixed the problem but I will give the points to someone who can give me a satisfactory explanation.

Hi all,
We have a very strange situation (this is not a technical question as I have found the fix but I do not like it). Anyway, we are using Exchange 2000 server. We recently found we had some problems sending Email to a few sites, and looking around internally I called the ISP to see if the problem was there. We found that the reverse DNS PTR record was missing. I also found the DNS setting on the Exchange virtual server was set to the server name as opposed to the MX alias. We also found a few other little things and rectified them all. This resolved the problem for all of the domains bar one.
I worked with their ISP and my ISP for quite a while to see if we could resume communication with this domain. After getting another vendor in the game he also found he was unable to send Email to this one particular domain.
He called me after a few hours and said the Email was successful when he removed the option to 'perform reverse DNS lookups on incoming mail'. I tried it and what do you know it worked. My question though was, why would performing reverse DNS on incoming Email prevent us from sending Email to 1 domain? More to that fact, why would incoming reverse DNS prevent us from sending full stop?
I posted the situation on the MS Exchange message board also and got a reply referring to reverse DNS being blocked by the recipient, but would that not cause problems with their Email to us as opposed us to them?
Strange forces at work here kids?!?!
Mike <

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by swade In reply to Exchange 2000 reverse DNS

I agree, I wouldn't like that fix either. I have been trying to resolve a problem with a sickening number of messages with return addresses of internal employees which are actually originating off-site. My SMTP filtering through ISA simply doesn't work.

You didn't mention if you had ISA running. Do you? And if so, have you looked into that?

Best of luck!

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by Jellimonsta In reply to

I have since given up getting to the root of the problem.

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by Jellimonsta In reply to Exchange 2000 reverse DNS

Hi Swade, thanks for the reply. We are not currently running ISA. I am due to impliment it in the coming months. As it stands the issue is purely within Exchange so it seems. It is not firewall or DNS related per se.
I am currently in contact with Microsoft and they are attempting to replicate the problem in order to find the resolution. I will probably post their findings here if they come to that resolution in order to save others this pain.

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by ariston In reply to Exchange 2000 reverse DNS

The one item that I can think of regarding reverse DNS lookups would be if the domain in question was actually some sort of forward instead of an actual domain. Think of it this way:

I send mail to That mail is forwarded to where it is deposited in the POP box. A reverse DNS lookup may not accurately identify the information for needed to verify that the mail can be delivered. By removing the reverse DNS lookup, the mail is sent without that verification and is delivered properly. You can almost consider as a "virtual" domain that simple exists to forward mail to a different location.

That's the best I've got !

Ariston Collander

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by Jellimonsta In reply to

Thanks for the answer Ariston, but the domain is not a forwarder. I have since given up getting to the root of the problem.

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by Jellimonsta In reply to Exchange 2000 reverse DNS

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