A command-line troubleshooting utility included with Microsoft Exchange Server. You can use mtacheck to check data stored by the Message Transfer Agent (MTA) in data (.dat) files.
These data files are related to problems with connectors that involve unprocessed messages. If mtacheck finds any problems, it tries to fix them. In a typical scenario, when an object in the MTA is damaged and blocks the messaging queue, mtacheck finds the object and removes it, placing it in a file so that you can examine it later.
You can also use mtacheck to try to restart the MTA if it stops and you can’t start it using the Services utility in Control Panel.