In Exchange 5.5, custom recipient's primary addresses are stored as X.400 addresses, but each custom recipient will also have an external Internet address. Many administrators are a little confused by this approach, and assume that something in the way the addresses are created by default causes X.400 addresses to be the primary address type. To that end, they may try to change a primary address from X.400 to an Internet address, and often believe the only way to accomplish this is by deleting the X.400 address and providing an SMTP address instead.
This approach backfires, unfortunately, and any custom recipient address modified in this fashion will throw back a "User Unknown" error when mail arrives for them.
Part of the reason for why Exchange 5.5 does this has to do with the reason for the existence of an X.400 address, which is used in Exchange 5.5 for describing where the object is in the Exchange directory, but not the address it uses for external e-mail. Delete the X.400 name in Exchange and you rob Exchange of the ability to know where the user account is in its own internal hierarchy, in effect making mail unroutable to that account. The e-mail address may be valid, but Exchange has no idea what to do with it anymore.
The best way to switch to SMTP as being the primary way to refer to custom recipients is to change the "E-Mail" address at the bottom of the custom recipient's General tab to be an SMTP address. If the custom recipient has one X.400 address, you can modify it so it looks like the X.400 addresses assigned by Exchange to the mailboxes. (If there are two X.400 addresses, make one of them the primary X.400 for the Exchange organization you're using, and either keep the old one as a secondary proxy address or delete it.)
Exchange 2000 uses Active Directory for its internal directory, and substitutes the X.400 internal addressing scheme with Windows' own GUID (Globally Unique Identifier) addressing. This way, an object can be renamed, moved to another organization or domain, or what have you, but it will still maintain a unique, internally-addressable identity that has nothing to do with its external e-mail address.
Serdar Yegulalp is the editor of the Windows 2000 Power Users Newsletter. Check out his Windows 2000 blog at www.thegline.com/win2kblog/ for his latest advice and musings on the world of Windows network administrators – please share your thoughts as well!
