Why did I get a message saying oops I have reached my limit ?

Why did I get a message saying oops I have reached my limit ? I am reply to email when I get this message.

I would like to inform you that Free accounts are limited to 20 reply/forwards per day. Once you reach that limit, you will have to wait until the next day to be able to reply/forward again. This limit was implemented to prevent the abuse of the reply/forward feature by spammers. 

You can choose to upgrade to a higher plan to increase the limit to 1,000 per day, or you can simply wait until the next day to reply to emails again. Regards.