Exchange SE 15.2.2562.46: MRSProxy returns HTTP 401 after successful NTLM authentication

I fixed this today, my post from Reddit below (the Microsoft Exchange Auth Certificate became lost / invalid)

--------------

Thank you for pointing me in the right direction! I replace the cert by simply clicking renew in Exchange ECP. After your post;

- Followed the MS instructions

- Followed MS article with Set-AuthConfig -PublishCertificate | Set-AuthConfig -ClearPreviousCertificate

- Reboot

- Found alot of Oauth errors still in Eventlog

- Removed old Auth cert after changing cert on the Send Connector, where it was still linked apparenty

-Reran the Hybrid Config Wizard

- Hybrid Config threw an error about being able to config Oauth

- Ran Steps 3, 4, 5 from https://learn.microsoft.com/en-us/exchange/configure-oauth-authentication-between-exchange-and-exchange-online-organizations-exchange-2013-help#step-3-export-the-on-premises-authorization-certificate

- Ran Get-IntraOrganizationConnector | Set-IntraOrganizationConnector -Enabled $true

After this it FINALLY started working. This might be a weird combination of old setup / config combined with this patch.