There are two ways of managing emails with Todoist:
- Linking to them from within a task
- Forwarding/sending them to a Todoist project.
The first option only allows you to open the message the same way you've added it, but the second one, which won't create a link, will convert the entire message to a task note.
This is indeed a Premium-only feature and you can read about both options and their advantages on our blog: http://todoist.com/blog/2013/01/zero-inbox-policy-with-todoist/