Sometimes when you try to add an smtp address to an object in AD, you get the following error due to the fact that the address already exists:
This email address already exists in the organization. ID no: c10312e7
Active Directory Users and Computers snap-in can be used to find the object that owns the address.
To do this, follow these steps:
1. Run Active Directory Users and Computers.
2. Right-click the domain object and choose Find from the context menu. This will bring up the Find Users, Contacts, and Groups window.
3. In the Find drop-down list, choose Custom Search.
4. Change the scope to Entire Directory
5. Click the Advanced tab and in the Enter LDAP query: field, enter the following text: proxyaddresses=smtp:firstname.lastname@example.org (use the email address that you are trying to add). Notice that the attribute proxyaddresses is plural, i always forget that…
6. Click the Find Now button and it will show you the object that owns the SMTP address. It’s usually a public folder in my experiences.