I have an exchange 2010 OWA just started giving error: "An Expected error occurred and your request couldn't be handled" after I click on inbox, option, forward etc. on OWA. I have reset all virtual directories and still gives me the error. It gives me an event ID 3.
Are you in the migration process of your Exchange to Exchange Online?
Be aware of customized solutions developed on the transport role on your old Exchange server. They might not be convertible to Exchange Online!
This video shows how to quickly and easily add an email signature for all users on Exchange 2016. The resulting signature is applied on a server level by Exchange Online.
The email signature template has been downloaded from: