Some of sharper readers of our documentation talking about schema changes that Exchange makes (see Exchange Server Active Directory Schema Changes Reference, November 2011) have noticed that in Exchange 2010 SP2, we have added several things that sound very related to what’s traditionally known as “custom attributes” in Exchange. Specifically:

For object class ms-Exch-Custom-Attributes we added:

  • ms-Exch-Extension-Attribute-16 to 45
  • ms-exch-extension-custom-attribute-1 to 5

There have been some questions regarding this; namely – are all of those for you to use? Does this mean that you now have all of those attributes to modify to your heart’s content? What’s the difference between all those things anyway?

Here’s the scoop:

For a while now, Exchange provides 15 custom attributes. Those are still there and you are free to use them as you used them before. They are known as CustomAttribute1 to 15 (or can also be referred to as ms-Exch-Extension-Attribute1 to 15). For more on those, please see this. So nothing has changed with those.

New! In Exchange 2010 SP2, we have added five new multi-value custom attributes that you can use to store information for mail recipient objects. They are the ExtensionCustomAttribute1 to 5 (also can be referred to as ms-exch-extension-custom-attribute-1 to 5). For the list of CMDlets that support those, please see this.

New! Finally, we have also added ms-Exch-Extension-Attribute-16 to 45. Those are not exposed to various CMDlets and Exchange management UI, because they were added for future use. As such, we cannot recommend that you use non-Exchange tools to edit their values because we might use those attributes in the future for various Exchange features. If and when we add management tools access to them, we will definitely let you know!

Read the complete blog at http://blogs.technet.com/b/exchange/archive/2012/01/17/custom-aka-extension-attributes-in-exchange-2010-sp2-and-their-use.aspx

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