We ran HCW >>> Exch 2016.
In a Hybrid Set up with O365.
Issue: Unable to send email from O365 to onprem.
- In the receive connector in the Edge onprem is the error; "454 4.7.5 Certificate validation failure, Reason: SubjectMismatch".
- Re ran HCW > No fix.
- Validated the Outbound connector from O365 to on-prem. It validated Ok.
- Test email was received by onprem user.
- Created a test user in the cloud with the initial domain (.onmicrosoft) and the user was able to send mail ok to onprem.
- Am suspecting the issue is with my custom domain.
- Because removing my custom domain from secure domains using set-transportconfig -TLSReceiveDomainSecureList $Null fixes the issue but this doesnot seem to be secure.
