I want to add subtask to a task I add via email (send email to a project).
Is that possible?
No, this isn't possible at the moment with email. Feel free to add it to our Votebox. http://todoist.com/Vote/
Can you add sub tasks via email now? Would be really great to have this feature? Where do I find all syntax and variables available in emails?
It's unfortunately still not possible to this yet. As for the which syntax are supported in forwarded emails, please refer to the image below: