This incident has been resolved.

“The Exchange Team has received reports this morning of AutoDiscover and certificate prompts from some Outlook clients. It was determined that one of the certificate auto-renew processes on the Exchange servers inadvertently removed the AutoDiscover service from the main Mail.umsystem.edu certificate. This has been corrected. If any users continue see issues, please have them restart their Outlook client or contact the Help Desk if they continue to see issues.”