DCE Failed to Transmit alert

[DCIM_Support]

Not sure if this is related to an earlier question I asked or not... 

We have noticed on our DCE server recently that emails are not being sent when alerts occur.  

Oddly, sending a test from the Email configuration page works, and 'system' emails (such as server rebooted, device disconnected etc) DO get sent OK too.  I also receive daily reports via email

If I test an alert action then the emails DO NOT get sent.

The NBC Logs contains these errors

[Message] FAILED TO TRANSMIT ALERT https://x.x.x.x:443/isxo/core/monitoring/central/AlarmEventReceiver org.soda.dpws.fault.DPWSFault: javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target [Emitter] com.apc.dpws.ISXCentralEventingNotifier

Nothing has changed on the server, the emails just stopped coming through.

The server is at version 7.6.0

I have created new Alert actions and Notification Policies to test against and cannot get any emails to be sent upon the occurrence of any device alarms or threshold alarms.

Please advise what the issue is here.  Is it related to the office 365 mail servers?

Regards

(CID:139692899)

[DCIM_Support]

Any help on this yet please?  Anyone?

(CID:140216903)

[DCIM_Support]

I guess not...

(CID:141270985)

[DCIM_Support]

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