Tested on Windows
In Outlook, the sender's email address is not shown in the message list, nor when you open a message. All you get is the sender's name. So, if a malicious person sent you a message from someone you know, you might not detect it.
1. Open Outlook
2. In your message list, click View (green arrow, below)
3. In the View ribbon, click on Change View (purple), then on Manage Views (blue)
4. Click on <Current View Settings>, then on Copy. (this will allow you to go back to your old settings if you wish)
5. Call the new view something like "Standard View", (you're free to change the "Can be used on" settings if you wish) and click OK
6. In the "Advanced View Settings" window, click OK. Your current view settings are now saved should you want to go back to them.
7. Click on <Current View Settings>, then on Copy again.
8. Call the new view something like "Domain View", (you're free to change the "Can be used on" settings if you wish), and click OK
9. In the "Advanced View Settings" window, click on Columns (blue arrow, below)
10. Click on the New Column... button (purple arrow).
11. In the "Name" field, type Domain. (as shown, lower right corner)
12. In the "Type" field, select "Formula"13. In the "Formula" field, paste in the following:
14. Click on the newly created "Domain" column (it will be at the bottom of the list on the right), and and click the Move Up button (green arrow) until "Domain" is just below "From" (orange arrow).
15. Click OK to close the "Columns" window.
16. Click OK to close the "Advanced View Settings" window
17. Click on the "Domain View" (under "View Name") and click Apply View.
18. Click OK to close this window.