To send email using Thunderbird you will have to modify your outgoing server settings. Start by going to Options and selecting Account Settings.
The Settings that need to be entered include:
Description - Easy-SMTP
Server Name - ssrs.reachmail.net
Port - 25, 2525, 465, or 587
Connection security - STARTTLS (25, 2525, 587) or SSL (465)
Authentication method - Normal password
User Name - Your email or accountkey/username