SMTP Relay with 365 Enterprise Mobility and Security

[Boredguy]

Since our EM&S licences were activated on Monday evening, we've noticed that the local SMTP relay server we use for our Powershell scripts, photocopiers and local web server has started reporting Authentication Unsuccessful errors in the log files.

 

The server had been happily connecting as a valid 365 user over port 587 for years with no issue so quite sure the EM&S is the issue.

 

I've already checked and set the SmtpClientAuthenticationDisabled value in the CasMallbox for the user to be $False as recommended by MS but still not connecting.

 

User logs in perfectly fine via the browser so I know it's not a user credential issue on that front.

 

Any ideas?