How to determine if there are duplicate SMTP addresses in Active Directory?

Reply 1)

If the SMTP address already exists within the organization, Active Directory Users and Computers informs you of this fact via the error message shown below:


Reply 2)

Simplest way to check will be type the address in outlook and hit ctrl+k. If the name get resolved the address is already in list. In case the name is hidden from Gal you can send a test mail with receipt to that address. If you receive the receipt the address is already existing.
Correct me if I am wrong.

Reply 3)

Alright, let me rephrase the question in the correct way.

Lets say we have a Domain Controller named, DC1 in India and another DC2 in US. Both these DCs are in their own AD sites and the replication is configured to happen in 3 hours.

An admin on DC1 is trying to create a user, say User1 with SMTP address of user1@domain.com and at the same time an admin in US is trying to create a user, User1 with SMTP address of user1@domain.com. What will happen when the 2 DCs synchronize?

Reply 4)

Logically Speaking … AD creates a conflicting (CNF:[GUID]) object if it finds the same object because of delay in replication. However as per the document

Duplicated SMTP Address
http://www.microsoft.com/technet/prodtechnol/exchange/guides/ExMgmtGuide/93733b19-b78c-4844-b263-04230026d9b6.mspx?mfr=true

Which says …
==============================================================================================================================================================================
When more than one mail-enabled object in Active Directory has the same SMTP address, the sender of an e-mail to any of those recipients will receive a non-delivery report (NDR) back with an NDR code of 5.1.4. (See Non-Delivery Reports.) The issue occurs because of the multimaster nature of Active Directory, when administrators create multiple mail-enabled objects on different domain controllers using the same SMTP address. If this occurs:
• Check to make sure no duplicated SMTP address exists in Active Directory.
• Consider using the LDAP Data Interchange Format Data Exchange (LDIFDE) tool to export the Active Directory database and search for duplicates.
==============================================================================================================================================================================

It seems .. it will create a Duplicate SMTP … but any one of them will receive an NDR.

Reply 5)

Exactly. Now, lets say we have lots of such duplicate SMTP addresses in our domain, resulting in loads of NDRs being generated. How can we find out which user names have got duplicate SMTP addresses? Any another method than using LDIFDE?

Reply 6)

I think we can also find using CSVDE. I will try to find command.
Correct me if I am wrong.

Reply 7)

You can use DUPSMTP.vbs downloadable from http://www.swinc.com/resources/ to achieve this as well.