I'm working on planning a new website registration process for a customer, moving from a single page to a multi-page form. As a first step, we capture the user email address in a similar way to Zagats.com

In the event of a user submiting their email but not proceeding with the rest of the registration, what would be the best practice for dealing with this partial data?

For instance - could one legitimately use the captured email address to contact the individual about completing their registration or should it just be permanently removed as they did not explicitly complete their registration.

Most of the resources I have found leave some room for doubt about this and so I was wondering if anyone knew of an established best practice?

Cheers,
Stuart