Emailing to Todoist - Referring to answer below for emailing to Todoist.
if you want to send tasks to Todoist via Email, you can find detailed instructions as well as the unique email address for each of your projects by clicking on the envelope icon at the top of any task list (visible from within any project).
If you're referring to the "Add email as task" function, please install the appropriate browser plugins (http://todoist.com/firefox or http://todoist.com/chrome ). If you're working on a different browser, you can use Todoist Anywhere.
After logging into your Todoist account on any of the browser plugins, please click on the "Show projects" link at the top and choose the project you'd like to add an email-task to. Once you enter the project, scroll down to the bottom of your task list and next to "Add task" and "Reorder", you should see a link saying "Add website as tasks" if you're browsing any website or "Add email as tasks" if you're viewing a GMail message.
This option is also available in the Todoist for Outlook plugin.