Is there a limit on the number of messages that I can send?

Free accounts are limited to 10 message sends to non-paid users for the lifetime of the account. A free user can continue to send secure emails by converting to a business account. 

There is no limit on the number of messages that a business account can send from the web portal or from our client applications. Standard business accounts are limited to 300 sends, per month, through our SMTP Service.