Microsoft has identified a couple of glaring issues with Exchange Online that can potentially cause customers problems.
The first issue is stale permissions due to deleted user accounts, and the second is a buildup of email because public folder pointers are no longer accurate.
To solve both of these issues, Microsoft has now deployed an automatic agent called the Public Folder Consistency Agent. There’s nothing customers need to do to utilize this new agent as it’s already been deployed and is currently running.
Per Microsoft, it runs on the following schedule:
For mail-enabled public folders, the agent runs every day to keep the MEPF updated and avoid any mail delivery issues. And stale permissions entries are checked for and removed once every 7 days.