Vessel is non-custodial, meaning no part of your email, password, or 6-digit PIN number ever gets transmitted to a remote server at any point. Separately, if you choose to take advantage of the email verification process in the digital identity tab of your passport, Vessel will see and use your email address for the sole purpose of verification.
Vessel also does store a set of derived private keys in an encrypted-at-rest format in a private extension storage, but these values never leave your computer at any point.