503 HTTP code error while trying to connect Outlook client to Office 365's configuration URL

Summary

Scenario: Connecting Outlook client to Office 365 Exchange server.

How to resolve the 503 HTTP error code returned to Guardian when connecting to the autodiscover configuration URL.

Problem

When trying to configure Outlook to connect to Office 365 Exchange server, HTTP code 503 is returned in Guardian for

https://autodiscover.yourdomain.com

Solution

Office 365 does NOT support HTTPS for the auto-configuration URL autodiscover.yourdomain.com.

You must use HTTP instead, that is,

http://autodiscover.yourdomain.com