Autodiscover fails after moving DNS to cloudflarefrom

Outlook to On-Premise Exchange 2016 Autodiscover fails after moving services to Cloudflare.

I’ve tried proxies and DNS only (grey cloud).

Microsoft Connectivity Analyzer:

"Testing the MAPI Address Book endpoint on the Exchange server.An error occurred while testing the address book endpoint.

Test Steps:
Testing the address book “Check Name” operation for user [email protected] against server An error occurred while attempting to resolve the name.

Additional Details:
A protocol layer error occurred. HttpStatusCode: 401"

Looking for suggestions.

Is your Autodiscover record a CNAME? If so, does it point to a hostname that’s proxied?

Yes, It’s a CNAME that points to proxy I think is disabled. ‘grey cloud’ set to DNS only.

If the entire chain is DNS Only, then you’ll have to track this down at the application and server level.

That was my first assumption - but the server passes self tests and local domain computers are Autodiscover-ing without issue. System has been in place since 2018. Moved to Cloudflare Monday, the first external Autodiscover failure was Tuesday. I’ll keep digging.

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