Nested Resources and Redirects

If I am keeping my resources at no more than one level deep how do I
redirect a user back to the appropriate controller?

Let's say I have Persons who can create Emails that have multiple
Email Items.

Persons > Emails > Email Items

After a person creates a particular email item for a particular email
how can I make sure they are redirected back the email that 1)belongs
to them and 2) is the current one they were working on?