How to disable Outlook Exchange autodiscover on macOS
While Autodiscover with Microsoft Exchange can be great, sometimes a company can have a rather difficult DNS setup. Maybe it's their use of internal and external DNS servers with different IP addresses and hostnames for the mail server if you're on the internal network or not. This can wreak havoc on Outlook's autodiscover feature. To disable Autodiscover, close Outlook completely, launch AppleScript, and type the follwing command (be sure to change AccountName to the profile name in Outlook. After you hit the play button to run it, you can close AppleScript and reopen Outlook. Autodiscover will now be disabled so whatever server settings you put in should stay.
tell application "Microsoft Outlook" set background autodiscover of exchange account "AccountName" to false end tell