You can use the same email
address if you choose however, you would need to create a new login for the
second tax return. We ask that you create a new login because if
you start another return under the original login it would overwrite everything
in the return you just filed. This would replace the original information and
you would be unable to retrieve the original return later if needed.
Please follow the steps in
the FAQ for instructions on starting another return
in TurboTax
Online.
https://ttlc.intuit.com/replies/3288574