Any information you provide on your passport renewal form can be given to any government agency, foreign government, corporation or private individual, who can then use it for “approved routine uses”, meaning basically anything the Feds feel like. From the “Privacy Act Statement” in the application:
This information may be disclosed to another domestic government
agency, a private contractor, a foreign government agency, or to a
private person or private employer in accordance with certain approved
routine uses. These routine uses include, but are not limited to, law
enforcement activities, employment verification, fraud prevention,
border security, counterterrorism, litigation activities, and
activities that meet the Secretary of State’s responsibility to
protect U.S. citizens and non-citizen nationals abroad.
You don’t have to provide your email:
Providing your Social Security number and other information requested on this form is otherwise voluntary.
But if you do, the one benefit is that they can use it to contact you:
If you choose to provide your email address in Item #6 on this application, Passport Services may use that information to contact you in the event there is a problem with your application or if you need to provide information to us.
Then again, they can also call or mail you if there’s a problem, so the upside seems pretty limited.
Credit:stackoverflow.com‘