We are running Exchange 2013 in a Hybrid Enviroment with Office 365 and we want to send all mails via Exchange Online. If we use the Outbound to Office 365 connector for all addresses (adding * at address space) we get the errormessage "451 4.4 0 primary target ip address responded with 454 4.7.5 Certificate validation failure."

What is the correct way to send all mails via Exchange Online or is that not possible?


We've just recently moved to a Office 365 Hybrid setup, but we've been using EOP for quite a while. I mention it because you might need to check the connectors in the Office 365 EAC to make sure they're setup properly. Specifically take a look at the Inbound connector (from Your organization to Office 365). It's likely setup to verify your connection through a certificate. Make sure it's the same certificate you have installed on Exchange.


Mentioned issue can occur because self signed certificate is used in Exchange 2013 server. check if you are using valid certificate.

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