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Reverse DNS problem with exchange server

Posted on 2009-05-06
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Last Modified: 2012-05-06
I'm getting this error on emails sent externally occassionally

There was a SMTP communication problem with the recipient's email server.  Please contact your system administrator.
            <mail.(mydomain).org #5.5.0 smtp;550 Reverse DNS lookup failed for host 206.184.xxx.98.>

When I look up the reverse DNS info on 206.184.xxx.98 on www.dnsstuff.com, I get the answer:
Answer:
206.184.xxx.98 PTR record: mail.(mydomain).org. [TTL 43200s] [A=206.184.xxx.103] *ERROR* A record for mail.(mydomain)l.org. does not point back to original IP (A record may be cached).

I changed the A record for mail.(mydomain).com to 206.184.xxx.98 so that it would point back to original IP as the message suggests, but then no mail came in, so I had to change it back.

If it helps, I believe our Netscreen firewall has a public IP of 206.184.xxx.98 and then four VIPs which are 206.184.xxx.99, 100, 101, 103

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Question by:tomcurrier
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Expert Comment

by:tenaj-207
ID: 24318477
The problem is your reverse DNS is set to a different IP address then what your email is coming in on.  So call up your ISP and have them remove the RDNS for 206.184.xxx.98 and move it to 206.184.xxx.103 for mail.(yourdomain).org.
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Expert Comment

by:Mestha
ID: 24319976
I would actually disagree.
It seems like your NAT is setup incorrectly. The traffic is coming in on one IP address and leaving on the other.
If you have your MX records point to one IP address then you need to ensure that there is a reverse DNS record on that address and the NAT is set correctly so the traffic comes out on that address.

Simon.
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Expert Comment

by:tenaj-207
ID: 24320901
Simon's right, as usual.

You need to change your MX record back to .98.  Then change your NAT router/firewall to pass email traffic (port 25) on to the server.

That should correct your NAT issue.
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Author Comment

by:tomcurrier
ID: 24321236
Thank you Simon and Tenaj.  This is where I run up against my newby-ness however.

'You need to change your MX record back to .98"  I'm not sure how to do this.  When I go to Network Solutions and then go to 'edit MX record', I can change the name of the mail server only.  There is no place to input an IP number.  Do you mean I should change the A record of mail.(mydomain).org back to 98 from 103?

Secondly, I don't know how to change my NAT.  We have a netscreen 25 and one of the Ethernet ports is IP 98.  Within this Ethernet 3, I have 4 virtual IPs, 99, 100, 101,  and 103.  103 is up and has Port 25 pointing to a Server which hosts NoSpamToday, from where our email is forwarded.

Many thanks in advance for your help.  
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Accepted Solution

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Mestha earned 500 total points
ID: 24328111
I wouldn't touch your MX records as that could impact on your email delivery. Leave the MX record setup alone.
Get your ISP to set the reverse DNS record on that IP address. Then you just need to get the NAT corrected. I cannot help with Netscreen - I haven't seen one for over 18 months.
Ask a separate question on that in one of the firewall zones.

Ideally what you want is a one to one NAT for the Exchange server. Of course that will presume if you are using OWA etc and on what IP address.

Simon.
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