Update - May 11, 2021: Updated with floor plan information.
Imagine you could book an office to work anywhere in the world. Now imagine this could be done in Outlook. Well, we have built a feature...
Updated May 11, 2021
Version 9.0
Blog Post
Also here:
'Microsoft Exchange Server 2013 includes 15 extension attributes. You can use these attributes to add information about a recipient, such as an employee ID, organizational unit (OU), or some other custom value for which there isn't an existing attribute. These custom attributes are labeled in Active Directory as ms-Exch-Extension-Attribute1 through ms-Exch-Extension-Attribute15. In the Exchange Management Shell, the corresponding parameters are CustomAttribute1 through CustomAttribute15. These attributes aren't used by any Exchange components. They can be used to store Active Directory data without having to extend the Active Directory schema.'
https://docs.microsoft.com/en-us/exchange/custom-attributes-exchange-2013-help
And on this very blog itself:
'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! 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 (Exchange 2010 SP2 or any later version) 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!'