The Message Transfer Service is the component of Exchange that handles the actual spooling of messages. Because of the diversity of its functions, many of the things that can go wrong with it are handled under fairly generic error reports that can cause confusion for an administrator trying to debug a problem.
One error which can be traced to several different possible causes is logged by Exchange with the notification "The recipient could not be processed due to congestion in the message transfer service" or another similarly-worded error. Here are several possible reasons for this:
- An Exchange 5.5 server is attempting to send a message to an MSMail recipient, which is having its mail forwarded through a bridgehead server, causing a bottleneck. To fix this, open the Registry on the bridgehead server and edit the key HKEY_LOCAL _MACHINESYSTEMCurrentControlSetServicesMSExchangeMTA Parameters; set the value Dispatch remote MTA messages to 0 and restart the Microsoft Exchange Message Transfer Agent service.
- An Exchange 5.5 server is attempting to send a message to a distribution list that has no Expansion Server defined. If a specific server was delegated as the Expansion Server and then deleted or taken offline, you may receive this error. To fix this, delegate a new Expansion Server by opening the properties sheet for the distribution list, select the general tab, and select a new Expansion Server in the Expansion Server list box.
- Bad network connectivity to an X.400 connector can cause this error, along with an ID 1294 error event that indicates a problem with ExchangeMTA / X.400. If this is the case, the retry timeout values for that X.400 connector may need to be bumped up. These values are found in the Connection Retry options section of the Override tab of the X.400 connector in question.
- If an Exchange server is removed from a particular site or organization and then reinstalled under a new site or organization, messages already in the queue sent to the server in its old configuration may not spool correctly and may eventually return a nondelivery report. The solution is to simply delete the messages sent to the old server and re-send them to the new one.
Serdar Yegulalp is the editor of the Windows 2000 Power Users Newsletter. Check out his Windows 2000 blog for his latest advice and musings on the world of Windows network administrators – please share your thoughts as well!