Our Exchange 2010 Server currently has 152 mailboxes and the License Summary says we need 152 Standard and Enterprise Cal's. After running a PowerShell script, it is the Searchable users that require the Enterprise Cal's. I understand that the Searchable Mailboxes are covered by the Standard Cal's in Exchange 2013 but is there an official kb or article from Microsoft detailing that searchable mailboxes are now covered by the Standard Cal's in Exchange 2010 as well?

Hi Williams,

You no longer require an Enterprise Client Access License (CAL) for Multi-Mailbox Search since October 1, 2012.

Exchange Server 2013 licensing

The following table provides a detailed feature breakdown for each CAL

Feature	Standard CAL	Standard plus   Enterprise CAL
Multi-mailbox   search	Yes	Yes

Exchange Licensing FAQ

 Q. Do Discovery Search Mailboxes (used to store multi-mailbox search results) require subscriptions?

 A. No.

Below Blogs can be considered as official References:

Announcing a licensing change for Multi-Mailbox Search

Update on Multi-Mailbox Search Licensing

If you are referring to Report Exchange Server 2010 Client Access Licenses (CALs) updated on 11/10/2009, it