What is Exchange Server Recipient Update Service (RUS)?

The Exchange Server Recipient Update Service (RUS) is responsible for maintaining address information about mail-enabled objects and for applying changes when you create or remove recipient policies (as described in the Microsoft article “XADM: How the Recipient Update Service Applies Recipient Policies“). If the RUS stops working, such changes won’t be applied correctly.

To know if the RUS is behaving badly, Check out the Microsoft article “How To Verify That the Recipient Update Service Is Working Correctly“.