Hello,
I set up auto forwarding years ago when I first had Outlook. Every time I upgrade to a newer version of Outlook it keeps that setting. The Problem is the email address that I auto forwarded to is gone. I deleted the rule in Outlook but every time someone sends me an email they get the "Mail System Error - Returned Mail". I get their email but they always get this message. Any ideas on how to fix this problem? Microsoft Support was no help at all. I have Professional Pro 2016.