"Mail can't verify the identity of the server"

Is my MacBook Pro at risk? A pop-up window came up saying Verify Certificate, mail can't verify the identity of the server "mail.mediacombb.net, the certificate for the server is invalid, you might be connecting to a server that is pretending to be "mail.mediacombb.net which could put your confidential information at risk.

njtozpxv13.mcomdc.com is at bottom.

Thank you I do not know what to do next.

[Re-Titled by Moderator]