Could not initialize class coldfusion.mail.MailImpl

We are upgrading from CF11 to CF2018.

We have update 2 applied. Whenever we access CFMAIL tag, we get exception "Could not initialize class coldfusion.mail.MailImpl".

Any ideas what might cause this?

I'm not  heavy into java, but I can't seem to locate where the coldfusion package is to see if the coldfusion.mail.MailImpl is defined ...

any help greatly appreciated.