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Reverse DNS error from remote hsot but all checks show I pass

Posted on 2013-05-24
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Last Modified: 2013-05-31
Hi,

we have recently moved office and servers and now I get the following from a remote mail server when we try and email a user there.


mx7.freeparking.co.uk gave this error:
"E5:Mail rejected because 178.251.239.149 doesnt have valid Reverse DNS."

When I run a DNS check at: http://www.intodns.com/letterpart.com

It's coming back showing that my Reverse PTR is ok.

Your reverse (PTR) record:
152.239.251.178.in-addr.arpa ->  mail.letterpart.com
You have reverse (PTR) records for all your IPs, that is a good thing.


Now. 178.251.239.149 is the IP address of the Exchange server but 178.251.239.152 is the gateway it sends through and what all tests, pings and sites show as the IP my server is sending from.

When I originally had 178.251.239.149 as the Reverse PTR. All the tests I ran showed it as failing so we had it changed to 178.251.239.152

Why is this one mail server complaining about my PTR while everyone else is happy and do I need to have 178.251.239.149 added as well to make it happy?
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Question by:Letterpart
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by:Ben Hart
Ben Hart earned 500 total points
ID: 39194097
According to MXToolBox:

220 EXCHANGE3.local.letterpart.com Microsoft ESMTP MAIL Service ready at Fri, 24 May 2013 13:23:33 +0100

Test      Result      Hide
      SMTP Reverse Banner Check      OK - 178.251.239.152 resolves to mail.letterpart.com
      SMTP Reverse DNS Mismatch      OK - Reverse DNS matches SMTP Banner      
      SMTP TLS      OK - Supports TLS.      
      SMTP Connection Time      0.874 seconds - Good on Connection time      
      SMTP Open Relay      May be an open relay.      Ignore
      SMTP Transaction Time      3.245 seconds - Good on Transaction Time      
Session Transcript:



MXtoolbox says you might be an open relay though.  And all DNS records for your mail.letterpart.com host should be pointing to your smtp gateway.
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by:Letterpart
ID: 39194113
Hi ubadmin

So my PTR is correct as I thought? I shouldn't then be getting errors from hosts expecting it on a different IP.

Open relay: So far all my checks show that I might be an open relay but when I checked the default receive connector I don't have "Externally secured" ticked on Authentication which is what I understand to be the correct way to do it?
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Ben Hart earned 500 total points
ID: 39194118
You should have an 'internet' connector, with the exchange servers IP selected, TLS and Anonymous Users selected.
You actually do not want Externally Secured enabled on any connector unless you have a specific reason.

More info here: http://social.technet.microsoft.com/Forums/en-US/exchange2010/thread/8d62ecc4-29ef-4ab3-a5ca-ed51fc4df802/
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