Having the email box not allow anything that isn't a regular email format(incorrectly entered) and allowing a checkbox to say NONE or DECLINED for the email to flag it as so.
It would be useful to one time document those with an email who decline to give.
It would be useful to document those without an email, to eventually follow up and check the status of them having an email.
It would make less work for those collecting going forward. With the changing landscape of healthcare apps, email is becoming one of the primary methods of contact/communication. Having standard emails in the system (NONE or DECLINED) assist with creating batch lists of patients emails and excluding others.