Sign in with Microsoft
Sign in or create an account.
Select a different account.
You have multiple accounts
Choose the account you want to sign in with.


Consider the following scenario:

  • You install Microsoft Exchange Server 2010 Service Pack 1 (SP1) in Hosting mode by using the /hosting switch.

  • You create two tenant organizations (organization 1 and organization 2) in the Exchange Server 2010 SP1 environment.

  • Organization 1 has a mail-enabled user (user A).

  • You create an external contact for user A in organization 2.

  • The administrator of organization 1 tries to manage the mailbox of user A by using the Exchange Control Panel (ECP).

In this scenario, the administrator receives an ECP dialog box that contains the following error message:

More than one mailbox has the same e-mail address. To resolve this issue, contact your administrator.


This issue occurs because the ECP incorrectly looks up the user by using a global scope. Therefore, two objects that have the same Simple Mail Transfer Protocol (SMTP) address are found.


To resolve this issue, install the following update rollup:

2661854 Description of Update Rollup 2 for Exchange Server 2010 Service Pack 2


Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

More Information

For more information about multi-tenant Exchange deployments, visit the following Microsoft website:

General information about multi-tenant Exchange deploymentsFor more information about the Hosting mode, visit the following Microsoft website:

General information about the Hosting modeFor more information about how to create a tenant organization, visit the following Microsoft website:

How to create a tenant organizationFor more information about the New-MailContact cmdlet, visit the following Microsoft website:

General information about the New-MailContact cmdlet

Need more help?

Want more options?

Explore subscription benefits, browse training courses, learn how to secure your device, and more.

Communities help you ask and answer questions, give feedback, and hear from experts with rich knowledge.

Was this information helpful?

What affected your experience?
By pressing submit, your feedback will be used to improve Microsoft products and services. Your IT admin will be able to collect this data. Privacy Statement.

Thank you for your feedback!