You will not be able to send e-mails until you have a verified e-mail address. To verify an e-mail address, go to DOMAINS inside the ADMIN section in your Dashboard and click “Add E-mail”. You will need to click on the link in your e-mail to verify it.
Please keep in mind that free e-mails (gmail, hotmail, yahoo, etc) will end up being trapped by Spam filters. It is best to verify a non-free domain (eg: firstname.lastname@example.org).