Daily limit exceeded

Hello, my account was no longer able to send emails, and after I logged in ZOHO, I noticed a message that said something like "your account has been blocked for exceeding the daily limit". However i unlocked it by filling a simple CAPTCHA.

I read somewhere that the limit of sent messages per day is 250 for a free account, but I have not come even close to that amount.
Could I have a more detailed explanation?
Thanks.