Apple Mail - myfairpoint.net server certificate invalid

Recently my Mac based Mail has stopped working for my two email accounts at myfairpoint.net, I get the Mail can't verify the identity of the server "mail.myfairpoint.net" error saying the *carrierzone.com certificate is invalid.

I am running Mohave (so I can still use iPhoto). Seems there used to be a way around this by an option to tell it to trust this certificate, but that option seems to have gone away.

I can still access the email via web browser, so the password is valid. I tried deleting one of the accounts in Mail then recreating it, and Mail then says "Unable to verify account name or password."