As you know Exchange 2010 SP2 Came with a requirement to update the schema,

Now quoting Michael’s Blog There are several very interesting items :

  1. The Mail-Recipient class has now gained the Company and Department attributes.
    This means that Groups (both security groups and distribution groups) and Contacts (mail contacts) can now be assigned values to the Company and Department attributes.
    From a technical perspective, the Mail-Recipient class is a system auxiliary class, for both the Group and Contact classes, and all attributes present in Mail-Recipient are available in them.

  2. The ms-Exch-Custom-Attributes class has gained 35 new custom attributes, from ms-Exch-Extension-Attribute-16 to ms-Exch-Extension-Attribute-45, and ms-Exch-Extension-Custom-Attribute-1 through ms-Exch-Extension-Custom-Attribute-5.
    This means that Contacts, Groups, Users, Public Folders, Dynamic Distribution Lists, and Recipient Policies all now have a huge number of new attributes that can be assigned arbitrary values by an organization. This is welcome news to organizations who are using many or most of the current custom attributes and are wary to extend the schema themselves.
    From a technical perspective, the ms-Exch-Custom-Attributes class is an auxiliary class for all the named classes above.

  3. Many new attributes and classes were added to provide support for Address Book Policies and to enhance access to various address lists, global address lists, and offline address lists maintained by Exchange.
    The master class is ms-Exch-Address-Book-Mailbox-Policy.

  4. There are several new attributes and one new class (ms-Exch-Coexistence-Relationship) that are probably designed to support the Hybrid Coexistence Wizard and to overall simplify the process of configuring hybrid coexistence with Exchange Online.

  5. There is a new class (ms-Exch-ActiveSync-Device-Autoblock-Threshold) and a number of new attributes that are within that class that appear to be designed to support automatic throttling of ActiveSync devices.

You can get a lot more detailes from the following link

Exchange Server Active Directory Schema Changes Reference, November 2011