Exchange Server 2000 SMTP Communication error : unable to verify address


I have a problem with a customers Exchange 2000 server.

When ever they send to a certain domain the mail always gets bounced back
with the following error

Your message did not reach some or all of the intended recipients.

      Subject:  Blah Blah
      Sent:     10/02/2003 12:13 PM

The following recipient(s) could not be reached:

      Joe Bloggs(E-mail) on 10/02/2003 12:15 PM
            There was a SMTP communication problem with the recipient's email server.  Please contact your system administrator.

            < #5.5.0 smtp;553 <> unable to verify address>


The doesnt seem to be a problem with any other recipients in other domains

It seems that the external server cannot resolve the exchange server name or something
like that but i dont know why it only happens which sending to a certain domain.

The A and MX records for the domain on the ISP seem to be OK

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Did you try to send the other one account of these certain domain ?

You said that no problem for other domain. In fact, your ISP could not verify this address. The recipient's domain is existing ? Can ping the address ?

Check it by following site

If existed, you may contact your ISP to look for anything had been happened in last few days for their DNS server.

I hope it can help.


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Jamie McKillopIT ManagerCommented:
The server you are trying to send to is attempting to perform a reverse DNS lookup on your domain and isn't able to. This is probably because you don't have a ptr record setup in your DNS for your mail server. Creatiing a ptr record should resolve this issue.
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Another issue with reverse DNS lookup is the ECN.  I have 2 companies I can't send email to from a server out of my control due to that server having ECN turned on.  Here is what one of those sites sent me on the ECN issue.  ECN can be turned on and off and is not required.

Here is what I got from Symantec - they sent me a beta patch and will probably put it in general release down the road.

"RFC 793 - which came out 20 years ago - indicated that there were certain bits of a tcp header that were reserved, and must be set to zero.  In a fairly recent trend, these reserved bits are being used for ECN packets (explicit congestion notification packets, typically in routers but also in Linux routing boxes) and, in some cases, web server communications, etc. As a result, the RFC mandate is being dissolved on a fairly global basis in a number of applications.  Because of this, we've had to change our stance on dropping these packets based on the RFC mandate - as it is increasingly possible that these packets represent valid network communications."
DingaAuthor Commented:
thanks for all the responses....i will try out the the different options and let everyone know the solution
You could try sending an email via a telnet session on their mail server.
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