400 4.4.7 message delayed

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400 4.4.7 message delayed

Case 1: After migrating Exchange 2003 to Exchange 2010, some emails can's be sent with 400 4.4.7 message delayed return message.

Troubleshooting: We found the Relay in the CAS server had an configuration issue. The Authentication was checked TLS. It should be Externally Secured (for example, with IPSec) as shown below.

Exchange configuration

Case 2: It is the Internal DNS Lookups issue. Please refer to this post: http://chicagotech.net/netforums/viewtopic.php?f=1&t=14007&sid=0ec4ac855cb9d0819fcb94bdb531412b.

Case 3: It is network issue. In our case, we have two CAS servers. We saw some emails in the queue until we fix the cas2 server network issue and reboot the server. Then all emails are sent out.

Case 4: It could be a network or routing issue. Check this link for more details: Move email queue from one Exchange server to another Exchange server.

Case 5: Your ISP may reject any message and require you to use their SMTP Server. Check this article for more information: Please follow this article to create a SMTP Relay using ISP SMTP server: How to create Send Connectors using ISP STMP Server

More cases can be found this post: 451 4.4.0 Primary target IP address issue n Exchange

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