Ok this is an old one. But quite a few still ask how to restore the M drive mapping to the Exchange2003 information store. Anyone moving from Exchange 2000 to 2003 certainly knows what I am talking about. Considering those migrating from Exchange 5.5 to 2003, this can be somewhat new to them. The M drive enables access to mailboxes and public folder items as if the information store was just another disk drive.

Before moving further its best if we remember the key reason why this drive mapping was removed. Access to the information store through this interface may damage (corrupt) the store database. For more details on M drive related trouble check the references below.

Despite this I have to admit that all my test Exchange machines have the M drive enabled. Clearly test machines are a disposable resource. Thus the power of this interface outweighs any corruption concerns. I also have to say that so far I never experienced corruptions that could be traced back to the M drive. This is probably due to my simple M drive usage rule. I only use the M drive for reading purposes. Whenever deleting or editing I simply switch back to Outlook or OWA.

The top reasons for using the M drive include:

• Easy extraction of emails in MIME format from the store.
• Quick access to all mailboxes for which I have logon rights without playing around with profiles.

Restoring the drive mapping just involves setting the following registry string value on the Exchange server machine:

Key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\EXIFS\Parameters
Value Name: DriveLetter

Setting DriveLetter="M" will restore the drive to its classic letter. You may also use any other free drive letter. Once the value is set just restart the Exchange Information Store service.

References

KB821836 - Drive M Mapping to IFS Is Not Present by Default in Exchange Server 2003

KB298924 - XADM: Do not back up or scan Exchange 2000 drive M