Error in Edge server mail queue LED=451 4.7.0 Temporary server error. Please try again later. PRX6

We have two Edge servers deployed at our Central location where it accepts mails from all other site and send it to Internet and vice versa. There is no problem for outgoing mails but while receiving the mails from the internet there is always an average queue of 600 to 700 mails (some time goes up to 2000). After analysing the issue we found the below errors..

  1. LED=451 4.7.0 Temporary server error. Please try again later. PRX6
  2. 451 4.4.0 SMTPSEND.SuspiciousRemoteServerError; remote server disconnected abruptly; retry will be delayed
  3. 421 4.4.2 Connection dropped due to TimedOut

We have then picked random 10/12 recipients from the error queue and found all of em  were  from a specific site.

we have tried the below solution... after searching for resolution on the Internet

  1. Tried enabling protocol logging but nothing found
  2. Since it was more likely to be a DNS issue, tried manually adding DNS server IPs in the Default front end receive connector properties.
  3. Tried adding DNS server IPs manually into both Transport servers in DNS Lookup setting in the server properties.
  4. Tried adding local server's IP to the hosts file.
  5. Checked if SMTP fixup is enabled on Firewall.
  6. Verified the receive connector security settings.
  7. Verified the CPU and Memory utilization is normal.
  8. Disabled the Performance Counter on both Transport Server to ensure memory usage.

but nothing seems helping

now the problem is because of this there is a mail delay of at least 20 minutes for incoming mails.

Need help resolving the same.

April 6th, 2015 6:01am

Run Get-TransportAgent | Disable-TransportAgent on the edge servers

Restart the transport service on the edge and see the results

You have already confirmed there is no issue with the firewall which is one culprit

If the above does not help then probably we can take a capture in wireshark,fiddler and identify to see where the packets gets delayed 

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April 6th, 2015 9:39am

Thanks for your response Sathish.

Will follow your suggestions and post the results. 

April 7th, 2015 10:20am

I have tried the above solution but didn't helped.. still finding queue on Edge server. :(

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April 8th, 2015 7:11am

I think its working now ..

after researching a lot on events on Transport servers we got to know that 'Default Frontend Receive Connector' was rejecting some messages...

we have then increased the value for the parameter "MaxInboundConnectionPerSource" from 20 to unlimited and MaxInboundConnectionPercentagePerSource from 2 to 10.. we have the waited for 2 to three hours .. the queue  then came down from 1500 to 5 and petty stable thereafter.

we will be monitoring the same for few days from now.  

April 9th, 2015 7:16am

Thanks a lot for posting the solution.

Glad to hear that it started working


Your hardware plays an important part in handling these message flow now.It shouldn't be a too small a disk and  Not enough memory 
Though 10 is not a high value make sure that above things are perfect and no mass mailers comes from vendors , external clients

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April 9th, 2015 1:26pm

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