Hello Exchange Experts,
couple of my customers have an exchange 2013 servers reported that they faced a strange issue in their exchange servers.
Some of sent emails for specific domains stuck in the queue shown an error as below:
‘400 4.4.7 Message delayed’ – Remote Server at Customerdomain.com (xxx.xxx.145.250) returned ‘441 4.4.1 Error encountered while communicating with primary target IP address: “421 4.4.2 Connection dropped due to SocketError.” Attempted failover to alternate host, but that did not succeed. Either there are no alternate hosts, or delivery failed to all alternate hosts. The last endpoint attempted was xxx.xxx.145.250:25′
Our Network team tried to check the firewall (Cisco ASA and Fortigate) by adding these specific domains to the white list, turn off SMTP inspection and stop AV and antispam in the firewall but no any solution solved the problem from the firewall side.
Now we re-think to solve the issue from the exchange servers side, I found that we can solve this issue from SMTP connector, as you know SMTP connectors are used primarily to connect to other mail systems or to define additional options for an SMTP Internet gateway. SMTP connectors can also be used to connect a routing group to another routing group internally, but an SMTP connector is generally not recommended for doing so. Essentially, SMTP connectors allow you to designate an isolated route for messages to flow either to a specific domain or over the Internet.
So, to solve this issue we forced the send connector which using to rout emails to internet to use HELO command by run -ForceHELO parameter as below:
Set-SendConnector “(connector name)” -ForceHELO $true
After executed the above command, the error in the queue change to be as below:
#501″FQDN” is invalid or DNS says does not exist
Now, to solve above error, Open Exchange 2013 ECP and follow below path:
Mail Flow -> Send Connector -> double click in the connector -> choose scoping tab
Now you will see that the FQDN is empty as below:
Just add your FQDN such as mail.yourdomain.com as below, then click Save:
If you have exchange 2010 you can do this by go to:
Organization Management -> Hub Transport -> Send Connector -> Double click in the connector and set the value as below:
After set this value, the message go out of the queue immediately after Restart the transport service, Again don’t forget to restart the transport service.
Ahmad is currently working in Specialized Technical Services Company (STS).