I receive a message says " Sorry, you have exceeded the daily limit of sending 500 email per day in your edition."

I receive a message says " Sorry, you have exceeded the daily limit of sending 500 email per day in your edition."

Der Zoho support team, 
I got the above message, I tried severl account that use defferent PCs still get the same message.
What I should do to resolve this problem?
please advise

Mohammed Bitar
Cinemana