XFOR: Outbound SMTP Mail Never Leaves Microsoft Exchange Server

Messages are not sent out over the Microsoft Exchange Server Internet Mail Service (IMS), they remain in the queue. It may look like the IMS is not functioning and restarting it will resolve this problem.

If you dump the status of the TCP connections to the Microsoft Exchange Server using the NETSTAT command, you will see several connections that are in the established state. You may also notice that these connections have been established for a long time.

Once a TCP connection is established, the IMS will timeout (5 minutes is the default time period) waiting for the banner to be sent. If the Banner doesn't arrive during this time, the IMS should terminate the connection and clean up the Socket. In this case, the connection count against the destination domain is being leaked and as a result, the IMS never terminates the connection and cleans up the socket.

Microsoft has confirmed this to be a problem in Microsoft Exchange Server version 5.0. This problem has been corrected in the latest U.S. Service Pack for Microsoft Exchange Server version 5.0. For information on obtaining the Service Pack, query on the following word in the Microsoft Knowledge Base (without the spaces):


Microsoft has confirmed this to be a problem in Microsoft Exchange Server version 5.5. This problem has been corrected in the latest U.S. Service Pack for Microsoft Exchange Server version 5.5. For information on obtaining the Service Pack, query on the following word in the Microsoft Knowledge Base (without the spaces):