Summary
This article explains how to identify External Sender Emails in Outlook Classic, New Outlook, and New Outlook (mobile).
Outlook Classic
For Outlook Classic, Central Washington University has an included an External tag and message banner inserted at the top of the email body message when receiving emails outside of the CWU.edu domain.

New Outlook and New Outlook (web)
For both New Outlook desktop and New Outlook web, Central Washington University has an included an External tag and message banner inserted at the top of the email body message when receiving emails outside of the CWU.edu domain.

New Outlook (Mobile App)
For the New Outlook mobile app, Central Washington University has an included an External tag and message banner inserted at the top of the email body message when receiving emails outside of the CWU.edu domain.

Additional Resources
Here is a related article on Dangerous Email - Identifying a Phishing Attack.
Submit a Service Request