How can I send a user registration confirmation email using Tornado and MongoDB?
I wonder why you would handle registration like that. The usual way to handle registration is:

Write the user info to the database, but with an 'inactive' label attached to the user.
Send an email to the user.
If the user confirms the registration, then switch the user to 'active'.

If you don't want to write to the database, you can write to a cache (like memcache, redis), then when the user confirms the registration, you can get the user info from the cache and write it to the database.
I'm working with Tornado and MongoDB and I would like to send a confirmation email to the user when he creates an account in my application.
For the moment, I use a simple XHTML page with a form and I send information to my MongoDB database using Tornado. I would like to have an intermediate step which sends an email to the user before inserting the data into the database.
I would like to know how could I send this email and insert the user account only after the user receives the email and confirms his registration.