Solving "e-mail address already exists in this organization" using LDAP query in ADUC

This dicussion was just in the newsgroups and I felt the solution was worthy of a blog post. A administrator is having a problem creating an SMTP proxy address for a mailbox. The message they get when they try to add snuffy@domain.com as an SMTP address is "This e-mail address already exists in this organization. ID no: c10312e7 Microsoft Active Directory - Exchange Extension".

The SMTP address the admin is trying to assign is already assigned to another mail-enabled object (mailbox, mail-enabled user, contact, or mail-enabled group.) I suggested doing an LDIFDE dump to LDF file of the entire directory and seaching through that file. Rich Matheisen suggested a better and far faster way.

Using the Windows 2003 Active Directory Users and Computers utility, right click on the domain, choose Find. In the Find: dropdown list, choose "Custom Search" and in the In: dropdown list, choose "Entire Directory". Click the Advanced property page and enter the following LDAP query (in my example, at least):

proxyaddresses=smtp:snuffy@domain.com

Click Find and you should find the object that already has that SMTP address. Thanks Rich!