You cannot create a new mailbox database if you already have 1000 mailbox databases in an Exchange Server 2010 environment

Assume that you have 1000 mailbox databases in your Microsoft Exchange Server 2010 environment. When you try to create a new mailbox database, the operation fails. Additionally, you receive the following error message:

This issue occurs because the New-MailboxDatabase cmdlet does not use the Lightweight Directory Access Protocol (LDAP) paged search when the cmdlet tries to retrieve the Active Directory system configuration session. However, the default maximum page size is set to 1000. Therefore, the Active Directory system configuration session returns ADSizelimitExceededException unexpectedly when you try to create the 1001th mailbox database.

To resolve this issue, install the following update rollup:

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

For more information about how to create a mailbox database, visit the following Microsoft website:
For more information about the New-MailboxDatabase cmdlet, visit the following Microsoft website: