454 4.7.0 Temporary authentication failureFurther investigation in the SMTP receive protocol log showed this error:
Inbound ExchangeAuth negotiation failed because of UnexpetectedExchagneAuthBlobLuckily based on some quick searches I was able to identify time synchronization as the source of the issue. Active Directory authentication starts to fail when time synchronization is not within 5 minutes. In this case the time difference was 6 minutes.
In the short term, I change the time on one server and verified that mail flow started to work properly. Long run I need to identify why time what not properly synchronized and fix it.
If you have DCs running on VMs, you may have to disable time synchronization on Hyper-V host, then correct DCs to sync with PDC server. Even though the time looks correct.
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