Exchange & Outlook 2019 AutoDiscover Fails

We have an internally hosted Exchange server on the company domain, domain joined clients are able to autodiscover our exchange server with no issues. We have a laptop that will not be joined to the domain but we still require access to the exchange server through outlook.

The issue is our domain is 'MyDomain.local' and the email addresses are '@Corporation.gov' and this non-domain joined machine is failing to autodiscover.

I have tried to override the hosts file to point from 'autodiscover.corporation.gov' directly to the exchange servers address but this does not work.

I have tried to edit the outlook registry settings on the effected machine using any combination of the following keys

ExcludeExplicitO365Endpoint 1
ExcludeHttpRedirect 1
ExcludeHttpsAutodiscoverDomain 1
ExcludeHttpsRootDomain 1

I have used this documentation to verify we do indeed have a SRV record setup https://docs.microsoft.com/en-us/troubleshoot/windows-server/networking/verify-srv-dns-records-have-been-created

And my initial troubleshooting was based off this documentation as well.. https://docs.microsoft.com/en-us/outlook/troubleshoot/profiles-and-accounts/unexpected-autodiscover-behavior

Testing autodiscover from within outlook always fails. Here in the test, the blanked out domain is 'Corporation.gov' which differs from our internal networks domain of 'MyDomain.local'.

I can point the effected machines browser at https://autodiscover.corporation.gov/autodiscover/autodiscover.xml (after doing the hosts redirect) and it pops up with a security certificate error asking me to continue, upon continue it then pops up with a username/password box asking me to login to get access to the page. If I type the username/password combination for the email address in question then it gives me access to the page.

I am wondering if the invalid security certificate and/or the autodiscover.xml page requiring me to login could be giving this issue?

Does anyone have any help/suggestions I've been trying to get this setup for about a week now and am racking my brain on it. Thank you very much for your time.

Solution 1:

Create a CNAME in your DC's DNS with hostname

mail.Corporation.gov

that refers to your Exchange hostname

exchange.MyDomain.local

than create an MX entry for domain

Corporation.gov 

that points to

mail.Corporation.gov

You also have to create a CNAME

autodiscover.Corporation.gov

that points to

exchange.MyDomain.local

Since your Exchange knows to be the final destination for the Corporation.gov domain, it shall correctly serve auodiscover functions to the laptop.
It is althought important that the configured DNS in the laptop is your DC.