Server Unauthorsed

I continually get a pop-up saying “server unauthorized”!

I have checked with my domain manager and the password is correct. I have Em Client on my laptop and desktop computers and get the same pop-up

What mail server account type is this eg: POP, IMAP, Exchange, Office 365 or iCloud ?

Also who hosts the mailbox ?

Also what version of eM Client do you have, and are you using Windows or Mac & OS version.