This article was previously published under Q280765
When you create a new user in the Active Directory Users and Computers snap-in and add an address in the Create Exchange Mailbox box, you may receive the following error message:
This e-mail address already exists in this organization.
This issue can occur if an object in Active Directory already has the address that you are attempting to add to the user's e-mail addresses list.
To resolve this issue, use either of the following methods:
Start the Exchange System Manager.
Click to expand the Recipients container.
Right-click All Address Lists, point to New, and then click Address List.
Click the Filter Rules button and verify that it is set to Exchange Recipients (the default setting).
Click the Advanced tab, click Field, and then click User.
Click E-mail Address.
In the Condition box, click Starts with, and then in the empty box to the right, type the first few letters of the address that you want to search for.
Check the lower window for matches.
If you find objects that have the same e-mail address as the one you are trying to add, either change the e-mail address for this object or delete the address if it is longer needed.
Repeat the same process for public folders, contacts and groups, but use the following modifications:
In step 5, point to User, and then change the setting to Public Folder, to Contact, or to Group.
In step 6, click E-mail Address or Alias if the E-mail Address option is not available.
If you have completed method one, and you did not find an e-mail address that is the same as the address that you want to add, use Network Monitor to do a trace between the Exchange computer and a workstation that has System Manager tools and Active Directory tools installed.
Start the Network Monitor trace.
Go to the workstation and re-create the error message.
Stop the Network Monitor trace.
Click Capture, and then scroll down to display the captured data.
Click Display, click Filter, and then double-click Protocol.
Click Disable all, and then in the right column, click to enable LDAP.
Click OK twice.
Look for a SearchRequest entry that has a detail window which lists the LDAP: Attribute Type. Under LDAP: Attribute Type, the following value is displayed:
LDAP: Attribute Value = SMTP: firstname.lastname@example.org
This is the address that you are trying to add to the user.
Go to the next pane in the Summary window. A SearchResponse entry is displayed which reports the object that owns the e-mail address in question. This information is found under: LDAP: ProtocolOP: SearchResponse. Expand the container until you find the following value:
LDAP: Attribute Value = CN=something, CN=something, DC=something
This object location owns the e-mail address in question.
Find this object in the Active Directory Users and Computers snap-in, and then change the e-mail address or delete this object if it is no longer needed.
For more information, click the following article number to view the article in the Microsoft Knowledge Base:
148942 How to capture network traffic with Network Monitor
In some scenarios, such as an ASP hosting scenario, there may be a need to create mail-enabled contacts in different OUs that have a common SMTP alias. EXAMPLE: CompanyA and CompanyB, both customers of an ASP, have their own address lists and cannot view the other customers' address lists. Both these companies have a common client, with common contact information. Using Active Directory Users and Computers, they cannot both create a contact with the same SMTP alias.
To resolve this, do not create the contact with Active Directory Users and Computers, but use the ADSIedit MMC snap-in or ADSI scripting (potentially from a web-based interface) to carry out this task. The fields to modify are "mail", "proxyAddress", and "targetAddress". Those fields can be modified to enter SMTP aliases that exist for other contacts in other OUs without error.