Updating host name in Outlook for Mac

• Open Outlook for Mac
• Click Tools > Accounts
• Select the desired email account
• Under "Incoming Mail Server" and "Outgoing Mail Server (SMTP)", modify the hostname.
• Click on the red X to close the window and save the new settings.

Note if you are using the NEW Outlook, you may not be able to edit those settings:

See if you can temporarily revert to using the Legacy Outlook

• Outlook Menu > Legacy Outlook.
  Update the hostname as shown above

Then switch back to the NEW Outlook:

• Outlook Menu > Uncheck Legacy Outlook.

If still using POP, and you have set up to leave mail on the server for X days: Outlook will re-download the mail present on the server.

Support for Outlook for Mac: https://support.microsoft.com/en-us/office/contact-support-within-outlook-for-mac-d0410177-8e65-4487-93f7-206a3a3d71a8