Topic Last Modified: 2005-11-18

The Microsoft® Exchange Server Analyzer Tool reads a series of registry keys to determine the level of message transfer agent (MTA) diagnostic logging set on the Exchange server. The registry keys reside at:


The default value for these keys is 0. If the Exchange Server Analyzer finds the value of any of these keys to be greater than 5, an error is displayed.

These registry keys are set by Exchange System Manager when you tune the logging levels on the Diagnostic Logging tab of a particular server's property page. Exchange System Manager lets an administrator set a specified logging level to None, Minimum, Medium, and Maximum. The corresponding values of the registry keys, respectively, are 0, 1, 3, or 5.

Therefore, a value greater than 5 can only be set by manually editing the registry, and should only be set at such a level during non-peak hours for very short debugging and troubleshooting. Setting these keys to integers above 5 heightens logging to debugging levels, which is extremely resource intensive. In addition to the debugging-level logging, setting these keys higher than 5 will output a "call.out" debug trace file every few seconds that is about 40 megabytes (MB) in size. This can fill the computer's event log in less than a minute.

The following table shows the MTA logging categories as they are listed on the Diagnostic Logging tab in Exchange System Manager and their corresponding key names in the registry.

Category as displayed in Exchange System Manager Corresponding registry key name

X.400 Service

1 X.400 Service


2 Resource


3 Security


4 Interface

Field Engineering

5 Field Engineering

MTA Administration

6 MTA Administration


7 Configuration

Directory Access

8 Directory Access

Operating System

9 Operating System

Internal Processing

10 Internal Processing


11 Interoperability

APDU (Application Protocol Data Unit)


The reference at the end of this article provides more information about what each MTA category logs.

It is recommended that you set the logging for each MTA category at None (0) unless you are actively troubleshooting. The reason for this recommendation is to maintain a manageable number of events being logged. Even a level of Minimum (1) will likely produce hundreds of event logs over the course of a few days, depending on the category where the level is set.

If you are not currently troubleshooting, it is likely that these values were set higher during a troubleshooting exercise and were inadvertently left set. You must set these values to at least Maximum (5), but you should consider setting the logging level to None (0) for each MTA diagnostic logging category unless you are actively troubleshooting.

To set the MTA Diagnostic Logging categories to none

  1. Start Exchange System Manager: Click Start, point to All Programs, point to Microsoft Exchange, and then click System Manager.

  2. In the console tree, expand Servers, expand the server that you want, and then click Properties.

  3. On <Server> Properties, click Diagnostic Logging.

  4. Under Services, click MSExchangeMTA.

  5. For each entry under Categories, set the logging level to none by selecting the category and then selecting None under Logging level.

  6. When you have set all categories to None, click Apply, and then click OK.

For more information about MTA diagnostic logging in Exchange 2000 Server and Exchange Server 2003, see the Microsoft Knowledge Base article 163033, "XCON: Description of Diagnostics Categories for MTA" (

For more information about MTA diagnostic logging in Exchange Server version 5.5, see the Knowledge Base article 163032, "XCON: Description of Diagnostics Logging for MTA" (