If we had a nickle for every time we get this question we would be millionaires.
I can tell you that in 99% of all cases your email is not down at all but rather your internet or network connection went down or was interrupted.
This begs the question: How Do I Know if My Email is Down or Not?
(1) Can you get online and visit websites?
YES = Go to #2
NO = Your Connection to the Internet is Down
(2) Can you access your Mail Server Online by going to mail.yourdomainname.com?