Reverse DNS lookup failed for host xxxx

We are getting this error occassionally (not often) when a user tries to send an email.  In the recent case, the CEO gets the same error whether sending from our local office email account (exchange) or from his corporate office email account (pop3).  He's having this problem sending to one external domain.  

I did a telnet (mail server IP) 25 and it seemed to be fine, with the same name and Ip as the MX record.

My DNSSTUFF.com account reveals that my reverse DNS seems to be ok.  Any idea what the problem might be?  
tomcurrierAsked:
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SurajConnect With a Mentor Commented:
you need to have a PTR Record for  your Connecting Ip address which your server uses to send mails out. Whatever you are think can be a good reason...
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shahsejalCommented:
Who is the gererating server of the NDR? Is it your server or the remote server?
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hau_itCommented:
Reverse DNS is a techinque that some companies deploy in order to avoid spam messages.
With that technique they try to make sure that the server that sending the mail exists and is no a spam message.
Create a ptr record in your dns server for your exchange host and try to see if you receive again the same error.

Dimitris
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SurajCommented:
Let me conform the issue.
you have issues sending mail to a perticular domain intermittantly.. and you get NDR intermittantly, Right?
1. could you paste the NDR here....
2. do this on command prompt
  nslookup
  set q=mx
  remotedomain.com

does it give you the MX / ip of the remote domain properly >??
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tomcurrierAuthor Commented:
Actually, I have additional information.  My ISP advises:  Is this likely the source of the problem?  We receive error messages sometimes, but nowhere near 50%.  

From your description of the problem, it seems that there are 2 reverse records in place for IP address xxxx

nets.yyyy.org.
and
mail.yyyy.org.

That will result in mailservers intermittently refusing to accept your mail since a query has a 50% chance of returning the wrong name for that IP and that in turn triggers anti spam measures on those server.

The IP in question was provided to you in a block assignment from Verio when you ordered the T1 line from them. If you wish for us to remove one of the PTR records please provide us with the name to keep and the name to remove along with the IP address. Once we have that information then we will forward it to Verio to make the corrections. Please allow 24-48 hours for this request to be completed.
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