XFOR: How the Internet Mail Service Handles Low Disk Space

ID: Q189587

The information in this article applies to:

Microsoft Exchange Server, versions 4.0, 5.0, 5.5

IMPORTANT: This article contains information about editing the registry. Before you edit the registry, make sure you understand how to restore it if a problem occurs. For information about how to do this, view the "Restoring the Registry" Help topic in Regedit.exe or the "Restoring a Registry Key" Help topic in Regedt32.exe.

SUMMARY

The Internet Mail Service (Internet Mail Connector in version 4.0) periodically (every 15 seconds) checks the amount of free disk space available on the drive that holds the spool directories. If free disk space drops below the configured threshold value (default = 10 MB), the Internet Mail Service goes into the Flush Mode until the free space rises above the threshold value.

This article discusses the Flush Mode and some registry values that can be modified to adjust the threshold value.

MORE INFORMATION

The Flush Mode prevents acceptance of new messages both from the Internet and the MTS-OUT queue. This does not affect the SMTP service or the content conversion algorithms. When the default threshold is met, the following events are logged in the application event log:


   SymbolicName=MSG_ENTERING_FLUSH_MODE
   EventType = Warning
   Category = Message Transfer
   LogLevel = 0
   The available disk space on the spool drive has dropped below %1
   kilobytes.
   The Internet Mail Connector will not accept messages for inbound and
   outbound conversion. Inbound and outbound message conversion will
   continue when the available disk space has increased above %1 kilobytes.

When the available disk space rises above the threshold, Flush Mode is turned off and the following event log message is logged:


   SymbolicName=MSG_LEAVING_FLUSH_MODE
   EventType = Warning
   Category = Message Transfer
   LogLevel = 0
   The available disk space on the spool drive has increased above %1
   kilobytes. The Internet Mail Connector is once again accepting messages
   for inbound and outbound conversion.

The threshold value can be reconfigured by adding the following registry value, using the procedure below:


   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeIMC
   \Parameters\DiskSpaceLowWaterMark  (DWORD).

Default Value: 0x00A00000 (10 meg in hex). When entering a new value, it should be done in Number of Bytes.

WARNING: Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk.

For information about how to edit the registry, view the "Changing Keys And Values" Help topic in Registry Editor (Regedit.exe) or the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe. Note that you should back up the registry before you edit it. If you are running Windows NT, you should also update your Emergency Repair Disk (ERD).

Start Registry Editor (Regedt32.exe).

Locate the following key in the registry:
```
      HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeIMC
      \Parameters 
```
NOTE: The above registry key is one path; it has been wrapped for readability.

On the Edit menu, click Add Value, and then add the following registry value: (Example: 20 megs 20 x 1,024,000 bytes = 20,480,000)
```
      Value Name: DiskSpaceLowWaterMark
      Data Type:  REG_DWORD
      Value:      20480000 
```

Quit Registry Editor.

Keywords : XFOR
Version : WINDOWS:4.0,5.0,5.5
Platform : winnt
Issue type : kbhowto