XCON: Performing An MTACHECK

This article provides steps for performing what is commonly called an MTACHECK. This document describes when to perform the procedure, exact steps for performing it, how to interpret the results, and what to do after performing the procedure. This article is a supplement to Knowledge Base articles:

When to Do an Mtacheck

MTACHECK checks the message transfer agent (MTA) database files in the MTADATA directory for consistency and integrity. MTACHECK can also remove directory replication messages, public folder replication messages, and link monitor messages. MTACHECK removes corrupted or inconsistent messages from the queue.

Perform an MTACHECK under the following circumstances:

• When you receive an event in the application event log (Event Viewer) which indicates that you should run MTACHECK to correct a problem.
• When you receive an event in the application event log, which suggests that there may be corruption in the MTA database. Always check the Microsoft Knowledge Base first for details on a particular Event ID.
• When the MTA queues are severely clogged with replication messages and no mail is flowing.

NOTE: MTACHECK is not a maintenance utility. It is a repair utility and should only be run to repair suspected or known corruption in the MTA database.

MTACHECK Utility

The following describes the MTACHECK command and optional switches.

NOTE: "mtacheck.log" is just an example of a logfile name. Any filename can be used.

NOTE: The /rd and /rp switches were first added to Mtacheck.exe with the Exchange Server 4.0 Service Pack 4 (SP4). The /rl switch was first added to Mtacheck.exe with the Exchange Server 5.0 Service Pack 1 (SP1).

MTACHECK Procedure

1. Confirm that the registry contains the correct path to the MTADATA directory. The key is: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet \Services\MSExchangeMTA\Parameters\MTA database path.
2. Stop the Exchange Server MTA.
3. IMPORTANT: Back up all \MTADATA\DB*.DAT files. DO NOT SKIP THIS STEP!
4. Confirm the backup by number of files and total size of the directory. NOTE: DO NOT delete the DB*.DAT files from the Mtadata directory.
5. From the \Exchsrvr\Bin directory, run MTACHECK.EXE /? to determine what switches are available. If at all possible, help the customer obtain the MTACHECK.EXE that comes with Exchange Server 4.0 SP4 or later.
6. Run MTACHECK.EXE with the preferred optional switches. See the "When to Use Optional Switches" section below.
   
   Depending on computer speed, this generally takes one minute for every thousand messages.
7. If MTACHECK completes with any errors such as
   

         Database repaired, some data may have been lost.
         - 0 queue(s) required repair out of 6 detected (0%).
         - 1 object(s) damaged out of 34 detected (2%).
   						

   
   delete all the files in the \Mtadata\Mtacheck.out directory and run the command again.
8. When MTACHECK completes successfully, it will display:
   

         Database clean, no errors detected.

9. Restart the MTA.

NOTE: Do not be alarmed by the "some data may have been lost ..." message. Objects and queues that were either damaged or corrupted were of two types: those that we don't mind losing (replication messages, link monitor messages), and those that could not have been salvaged anyway. Replication and link monitor messages are naturally regenerated, and hence are expendable. Simply repeat the MTACHECK command until you receive the message "Database clean, no errors detected."

When to Use Optional Switches

Use the following guidelines for deciding when to use an optional switch:

1. Reducing the size of the MTA database.
   If you want to reduce the number of DB*.DAT files in the \MTADATA directory, use the /rd, /rp, and /rl switches serially. In other words, first run
   
   MTACHECK.EXE /rd
   
   and let it complete. This will eliminate any directory replication messages currently in the MTA database. Then run
   
   MTACHECK.EXE /rp
   
   to eliminate public folder replication messages. Finally, run
   
   MTACHECK.EXE /rl
   
   to eliminate any link monitor messages.
2. Quick integrity check.
   If you want to perform a quick integrity check of the MTA database to see if any DB*.DAT files are corrupt, simply run MTACHECK.EXE with no optional switches. If any corrupt files are found, they will be moved to the \MTADATA\MTACHECK.OUT directory.
3. Gathering details on the MTA database.
   If you want to get details on the MTA database, such as the number of static queues, the ID of a particular queue, or the exact objects currently stored in a particular queue, run
   
   MTACHECK.EXE /v /f mtacheck.log
   
   This will generate a text file named Mtacheck.log in the directory you ran MTACHECK.EXE from (usually \Exchsrvr\Bin). This text file is an invaluable resource when you are attempting to track a specific object in the MTA.

What to Do Next

You can expect the MTA to take several minutes to rebuild queues after doing an MTACHECK. After performing an MTACHECK, you should monitor the MTA to ensure that the errors you encountered prior to the check have been eliminated. An MTACHECK should be considered a solution only when it permanently eliminates the problem it was attempting to fix. If the problem recurs, you should follow other procedures to further troubleshoot.