cant get my. mac email to go online. Something to do with cetificates

I cant get my email .mac email to go online. All my settings are correct. It keeps flashing up : Mail was unable to verify the identity of the server, which has a certificate issued to "mail.mac.com. The error was: An SSL error occurred while trying to read data from the server"mail.mac.com" It's driving me crazy, e-mails are coming through fine on my iphone, and the pop accounts on the same mac.