Problem with mail delivering via SSL error 454 4.7.4

[Jozi Zurbej]

Hi we have problem with delivering mail from fortimail appliance to exchange 2016 infrastructure, sometimes emails stuck at fortimail and not delivered to exchange with this message: 

dsn=4.0.0, stat=Deferred: 454 4.7.4 temporarily failed to deliver message via SSL/TLS.(Reason:454 4.7.4 temporarily failed to deliver message via SSL/TLS.)

this errors ocasionally occurs and emails are going to timeout and not delivered after few days,

I cannot find nothing about this error code, and to troubleshoot.

Thank you

[#2]

@Jozi Zurbej 

Hi,

The issue can be caused by one of the following reasons:

• The Exchange server is experiencing Time synchronization issues.
• There is a replication issue between the domain controllers.
• The Exchange server is experiencing Service Principal Name (SPN) issues.
• The required TCP/UDP ports for the Kerberos protocol are blocked by the firewall.

https://docs.microsoft.com/en-us/exchange/troubleshoot/client-connectivity/454-4-7-0-temporary-authe... 

https://www.thecloudtechnologist.com/how-to-fix-exchange-online-hybrid-outbound-connector-454-4-7-5-... 

Regards,

MD