I often hear customers who run an onpremises Exchange 2010 or 2013 environment in Hybrid mode with Office 365 complain about their Shared Mailboxes not appearing in Office 365 when using AADSync (or AADConnect).
This is important for mail routing if they don’t exist as contacts, or if you are using Exchange Online Protection for these mailboxes.
So, two quick steps to configure AADSync to also sync disabled users to Office 365.
1. Open the Synchronization Rules Editor on the aadsync server and edit the inbound rule called User AccountEnabled
Voila, your disabled useraccounts will now properly sync to Microsoft Office 365.