When setting up DirSync (Active Directory Syncronization) between your Office 365 Hosted Exchange and your on-site Server 2012 Active Directory, you may find that you are missing attributes in the local AD that will sync up to the cloud. This may become an issue if you want to use Dynamic Distribution Groups within Office 365.
The reason this occurs is that certain attributes like ExtensionAttribute 1, 2, 3, etc, are attributes associated with Exchange and not your normal AD Schema. This quick fix is easy and painless and should only take a couple minutes.
First, download Exchange 2010 or 2013 to your primary AD server. You don’t need to pay for it, but it might want you to register with an MS account (no big deal.) Extract the install after the download. Next, run Windows PowerShell as an Administrator and navigate to the folder where the Exchange download resides. Run the following command:
.setup /preparead /OrganizationName:exchange.
(You may need to play with the switches as we found they respond different with different versions of PowerShell.)
Finally, when the setup is complete, navigate to one of your user accounts in AD, right click and select properties, select attributes and just like magic, you should see additional attributes that will sync up to your Office 365 account.
(Note: Running the
setup /preparead command will only extend your schema and not install Exchange. Also, the organization name is required for this command to function, however the name you use is irrelevant because you are not setting up an instance of Exchange onsite.)