Allow longer contract duration than 12 months

Hey, any chance you guys could please allow us users to buy Mailbox subscription for more than 12 months at a time? Currently it's possible to pay for only 1 month or 12 months in "All settings > Contract and payment > Payment" after logging in. I would possibly like to buy a longer subscription than 12 months. Perhaps add an option to choose 24 months or maybe even 36 or more?

Thank you for your consideration.

P.S. If I currently want to buy more, can I stack up 12 month periods multiple times?