XGEN: Troubleshooting the MTA Queue to the Internet Mail Service

If the Message Transfer Agent (MTA) queue to the Internet Mail Service is running slowly or not at all, it can be a difficult issue to troubleshoot. This article offers some procedures that may be helpful when trying to resolve this problem. It assumes that the MTA, Information Store, and Internet Mail Service services are processing other mail including mail between mailboxes on the same information store, mail to other servers in the site, and mail across other connectors.

When you see mail in the MTA queue (through Performance Monitor or the Microsoft Exchange Server Administrator program), that mail is still in the form of a .dat file in the Exchsrvr\Mtadata folder. The next stop for this mail is a hidden system folder called Mts-Out, which is the folder used by the store for message conversion from MDBEF (Exchange) format to SMTP format. The mail gets to the Mts-Out folder by means of XAPI calls between the MTA and the information store.

If there is a problem with mail moving from Mtadata to Mts-Out, there are several things you need to check.

1.	Are there any errors or warnings from the Internet Mail Service, MTA, or information store that may relate to slow outbound SMTP mail flow?
2.	What are the values at the following registry locations? You may need to increase these values. HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeIS\ParametersSystem\BACKGROUND THREADS HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeIS\ParametersPrivate\GATEWAY IN THREADS HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeIS\ParametersSystem\MAX THREADS (Public + Private) "Gateway In Threads" is the number of threads the information store creates on behalf of the Internet Mail Service when the Internet Mail Service logs on to the information store. "Gateway In Threads" moves messages from the MTA into the information store's Mts-Out queue (destined for the Internet Mail Service). "Gateway Out Threads" moves messages (coming in from the Internet Mail Service) out of the information store's Mts-In queue on to the MTA for distribution. So, increasing the "Gateway In Threads" values increases the pipe between the MTA and the information store for outbound Internet Mail Service messages. Change to 0x8 (hex) = 8 (dec). NOTE: Gateway in/out threads are used by the information store for any gateway, not just the Internet Mail Service. The "Background Threads" and "Max Threads <Public+Private>" values must be increased accordingly if you increase "Gateway In Threads" value.
3.	Turn up logging on the MTA and the Private Information Store. Double-click the MTA to open the properties, click Diagnostics Logging, and under Categories, click X.400 Service, Interface, Field Engineering, and Internal Processing, and set each to maximum. This generates much more MTA logging and also dumps AP logs in the Mtadata folder. On the Private Information Store Properties page, under Services, select MSExchangeIS and Private. Under Category, select the following Transport Sending and Transport Delivering, and set these to maximum. This generates Snd*.logs and Dlv*.logs in the Mdbdata folder. The application log size should be at least 30 MB, overwrite as needed.
4.	Create a Calls.out file from the MTA, preferably with a "debug" MTA (instructions for this can be found in Microsoft Knowledge Base article, Q178531, "XADM: Generating the Calls.out File," listed below). This file details the state of the MTA at the time of the problem.
5.	Send Microsoft Support Professionals the requested data (app log, AP logs, Snd*.logs, and Dlv*.logs from the Mdbdata folder, Calls.out file, and registry configuration information).

For additional information, please see the following articles in the Microsoft Knowledge Base: