XCON: Move User Operation may Cause Mail to Stall or NDR (172364)

SYMPTOMS

During a move user operation, messages sent to users that are being moved from one Microsoft Exchange Server to another may result in a Non Delivery Report (NDR) or the message being stranded in the Microsoft Exchange Server Message Transfer Agent (MTA) queue.

The NDRs will look similar to the following:

From:System Administrator
To:JoeUser
Sent:Thursday, April 02, 1998 8:09 AM
Subject:Undeliverable: RE:
Your message did not reach some or all of the intended recipients.

Subject:RE:
Sent:4/2/98 8:09 AM

The following recipient(s) could not be reached:

JoanneUser on 4/2/98 8:09 AM
Unable to deliver the message due to a communications failure
MSEXCH:MSExchangeMTA:50site:SERVER50

CAUSE

During normal operation, the MTA will perform address lookups against the Microsoft Exchange Directory to determine the location of message recipients. When a user is being moved, the MTA may read the Directory and think the user is located on their original Server, when in fact the user has now been moved to the new Server. When this happens, the originator will receive an NDR stating that the user name was not found.

When both the originator and recipient are being moved and this happens, the message may become stranded in the Private Information Store queue.

There is a very small window of opportunity for this problem to occur, but the window does exist.

WORKAROUND

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.

There are two things the Exchange Administrator can do to prevent this problem from occuring:

Perform the move user command when the users are offline. If there is no mail being processed, this problem will not occur. This is the recommended method. -OR-
Start the Windows NT Registry Editor and go to the following key:
```
   HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeMTA\ 
   Paramters\ds_read cache latency (secs)
						
```
By default, the MTA will cache Directory entries for up to 60 seconds to speed address resolving. By setting this to 0, the MTA will always make a call to the Directory. This solves the above issue, but has the price of impacting system performance.

If this method is performed, it is recommended that after you make the change you stop and restart the MTA service and move the users. After the users have been moved, edit the registry entry again, set it back to the default, and stop and restart the MTA service.