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SMTP/Reverse DNS-Exchange problems

Posted on 2004-08-03
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Last Modified: 2010-05-18
I have Exchange 2003 and appear to be having reverse DNS lookup problems or possibly SMTP configuration issues. We can send email to any destination when we have a smart host specified in SMTP properties but experience return emails from specific destinations (ex. hotmail accts) when not using a smart host.

I want to permanently remove the smart host setting but cannot until I resolve the issue.

note: when not using smart host: return emails specify our local domain mail.gcps.local verses mail.greensville.k12.va.us which we are suppose to see.


Thanks
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Question by:mtmor
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4 Comments
 
LVL 21

Expert Comment

by:marc_nivens
ID: 11707459
It sounds like your IP is blocked by the receiving servers for some reason (probably open relay).  Going through a smarthost will bypass this since they receive the mail from a different IP.  Go to http://www.ordb.org/lookup/ and search for your IP to make sure you're not listed as an open relay.

If thats not it, can you tell us the text of the NDR?
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LVL 36

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by:
grblades earned 250 total points
ID: 11707560
Hi mtmor,
It could be a number of issues causeing the problem. I suggest you check and fix all these :-

1) IP blacklisted as marc_nivens described. I have also found this site usefull for checking multiple lists http://rbls.org

2) IP is a dynamic IP address and it is in a database of dynamic addresses. To get around this you have to either get a fixed IP address or use a smart host.

3) You mail server is advertising the wrong name. It looks as if you have this problem. You need to make sure your email server advertises its name as mail.greensville.k12.va.us when it connects and issues the EHLO command when sending an email. I am not sure how to do this in exchange.

You should also check that a DNS lookup on your IP address resolves to mail.greensville.k12.va.us aswell as often this is also checked by receiving mail servers.
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Author Comment

by:mtmor
ID: 11708447
Iv'e already checked the blacklist sites and no signs of this being the problem, IP is fixed and DNS reverse lookup appears to work fine.

However, It appears the firewall (router) was causing the problem...Thanks anyway!
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LVL 3

Expert Comment

by:prav007
ID: 11892067
Some websites the best example aol.com does not accept mails from mail servers which do not have reverse dns lookups configured for their ip addresses.

Might be your firewall is natting the ip address and there was a problem with NAT .

At one site I had faced such a problem and found out that the ISP was supposed to make a reverse dns entry for a company since they had hosted their dns servers at the ISP. Once this was done the problem vanished . The other solution is to use the ISP's SMTP server as a smart host . However in this case u r totally dependent on the ISP.

Best Regards,
Praveen
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