How to Set the Compatibility Registry Value for POP3 Users
Internet messaging client computers that access Exchange Server using Post Office Protocol version 3 (POP3) use the streaming store (.stm file) for reading and writing mailbox data stored as Multipurpose Internet Mail Extensions (MIME) content. If you use the Move Mailbox functionality in Exchange System Manager or the Active Directory Users and Computers snap-in to move a mailbox that is accessed by a POP3 client, the data in the moved mailbox is promoted into the Extensible Storage Engine store (.edb file), and the content is converted from MIME content to MAPI content.
When the POP3 client logs on, exact message sizes are calculated, and MAPI-to-MIME conversion of the mailbox data occurs in memory and on the disk of the server. The conversion on disk occurs in the Windows TMP folder, which is usually not on a disk that has a large number of spindles. The disk cannot handle the large number of input/output (I/O) requests caused by a conversion of so many messages. Therefore, a user may experience long delays (up to several minutes) when the user does something as simple as switching between messages on the client. This behavior occurs because the disk that the TMP folder is located on cannot keep up with all of the disk activity that Exchange generates to convert messages. One way to avoid the adverse effects of this behavior, you can move the TMP folder to a disk that has a high-performance caching controller connected to it and enough spindles to handle the conversions. For detailed instructions about how to move the TMP folder, see How to Move the TEMP and TMP Directories.
In extreme cases, very large temporary files may be created on the Exchange server when this behavior occurs. In some cases, without proper planning or available server resources, the conversion from MIME to MAPI may also cause system latencies. This may cause POP3 clients to experience long delays during logon because of the requirement for exact message size calculation. You can improve performance by adding the Compatibility registry value to the Exchange server(s) containing mailboxes accessed by POP3 clients.
Before You Begin
Before you perform the procedure in this topic, be aware that the procedure contains information about editing the registry.
Warning
Incorrectly editing the registry can cause serious problems that may require you to reinstall your operating system. Problems resulting from editing the registry incorrectly may not be able to be resolved. Before editing the registry, back up any valuable data.
Procedure
To Set the Compatibility Registry Value for POP3 Users
Open a registry editor, such as Regedit.exe or Regedt32.exe.
Navigate to HKLM\System\CurrentControlSet\Services\Pop3svc\Parameters.
Right-click Parameters and click New | DWORD Value.
Name the new DWORD value Compatibility.
Double-click Compatibility.
Set the Base to Hexadecimal.
In the Value data field, enter 0xfffffffe.
Close the registry editor, and then restart the Microsoft Exchange Information Store and IIS Admin services for the change to take effect.
For More Information
For more information about client latencies and the Compatibility registry value for POP3 clients, see Microsoft Knowledge Base article 317722, "Client latencies occur when Exchange 2000 Converts Mail from MAPI to MIME format" (https://go.microsoft.com/fwlink/?linkid=3052&kbid=317722).
For information about how to edit the registry, see Microsoft Knowledge Base article 256986, "Description of the Microsoft Windows Registry" (https://go.microsoft.com/fwlink/?linkid=3052&kbid=256986).