Ramdom NDRs - There was a SMTP communication problem with the recipient's email server.

For  while now, different users around the office are ramdomly receiving bounce backs when sending emails through their Outlook 2003 client / Exchange 2003, with the error being;;

   There was a SMTP communication problem with the recipient's email server.  Please contact your system administrator.


When I check eventvwer on exchange server I find this error;


A non-delivery report with a status code of 5.5.0 was generated for recipient rfc822;acct.??@???.????.com (Message-ID <242749538A520140A585FCF03D46FCB10104F86C@??????-srv01.unsworthcl.com>).  
Cause:  This message indicates a generic protocol error (SMTP error).  For example, the remote SMTP responds to an issued EHLO with a 500 level error and the sending system will QUIT the connection and report this with NDR indicating the remote SMTP server cant handle the protocol.    
Solution:  View the SMTP log or run a netmon trace to see why the remote SMTP server rejects the protocol request.

For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.


I have run SMTP Diagnostics at mxtoolbox.com

RESULT: smtp1.unsworthcl.com
Banner: SMTP ESMTP [156 ms]  
Connect Time: 3.062 seconds - Good
Transaction Time: 3.812 seconds - Good
Relay Check: OK - This server is not an open relay.
Rev DNS Check: OK - 83.104.227.178 resolves to uglog2-adsl.demon.co.uk
GeoCode Info: Geocoding server is unavailable
Session Transcript: HELO please-read-policy.mxtoolbox.com
250 SMTP [141 ms]
MAIL FROM: <test@mxtoolbox.com>
250 ok [156 ms]
RCPT TO: <test@mxtoolbox.com>
553 sorry, that domain isn't in my list of allowed rcpthosts (#5.7.1) [141 ms]
QUIT
221 SMTP [156 ms]
 

RESULT: smtp2.unsworthcl.com
Banner: SMTP ESMTP [250 ms]  
Connect Time: 0.344 seconds - Good
Transaction Time: 8.375 seconds - Not good!
Relay Check: OK - This server is not an open relay.
Rev DNS Check: OK - 80.177.32.174 resolves to mailgate.unsworthcl.com
GeoCode Info: Geocoding server is unavailable
Session Transcript: HELO please-read-policy.mxtoolbox.com
250 SMTP [3375 ms]
MAIL FROM: <test@mxtoolbox.com>
250 ok [359 ms]
RCPT TO: <test@mxtoolbox.com>
553 sorry, that domain isn't in my list of allowed rcpthosts (#5.7.1) [3766 ms]
QUIT
221 SMTP [281 ms]
 


I cannot identify problem, please help.
uklogisticsAsked:
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bevhostConnect With a Mentor Commented:
It would be nice to know what the actual 500 error message text was.
Is that in the bounce back message?

It could be that your PTR records aren't setup quite right.
The PTR record should have a matching A record that points back to the same IP address and this should match the EHLO name or FQDN of the exchange server.

If you have multiple mail servers NAT behind one firewall create multiple PTR records for the same IP.

Many exchange servers announce themselves as servername.mydomain.local which cannot be found in the DNS.

To check this in your exchange go into Exchange System Manager
Expand Servers->SERVERNAME->Protocols->SMTP->Default
Right Click then Properties
Delivery TAB
Advanced Button
change the fully qualified domain name to match your DNS entries.

See section 2.1 or RFC1912.
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uklogisticsAuthor Commented:

No the error doesn't appear in the bounce back, and i'm not too sure why; Is there any way I can check?


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

      Subject:      FW: ?????????????
      Sent:      13/06/2008 10:50

The following recipient(s) could not be reached:

      '??.??@???.???.com' on 13/06/2008 10:50
            There was a SMTP communication problem with the recipient's email server.  Please contact your system administrator.
            <unsworthcl.com #5.5.0>

It appears the Fully Qualified Domain name is already present , and appears correct : unsworthcl.com
see screen shot

http://img71.imageshack.us/img71/7886/smtpserverpropertiesgk0.jpg
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cshepfamConnect With a Mentor Commented:
You may be under an NDR attack:


http://support.microsoft.com/kb/886208
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bevhostConnect With a Mentor Commented:
You could try relaying your outbound mail through a smart host which will always accept your mail and perhaps has better logging and or more understandable bounce messages.
If you want a free windows bases SMTP server see http://www.hmailserver.com/
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uklogisticsAuthor Commented:
Hi
My ISP is Demon, and we smarthost to post.demon.co.uk as shown in attachment . From what I understand, Demon smarthost are just providing a generic smtp error :  #5.5.0 . I'm i correct?

If that is the case, can anyone recommend another smarthost I could use, as suggested by bevhost, who might be more reliable and provide understandable bounce errors?

thanks


smarthost.gif
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uklogisticsAuthor Commented:
I have identied a common pattern . These NDRs appear to occur at peak times of the day, when larger than usual emails are in/out . Could this be related to the number of concurrent connections my smarthost (post.demon.co.uk) will allow at any one time. Is there anyway I can do to exchange to test that this is the case?
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