As part of the iOS 10 update, the Apple Mail app now includes an unsubscribe option at the top of marketing email messages that allows the recipient to unsubscribe without scrolling to the bottom of a message. This information is included in a mail header called 'list-unsubscribe' (more info here).
HubSpot supports this and includes it out of the box. When a recipient clicks the unsubscribe link at the top of an email sent through HubSpot, the contact will be automatically opted out of all email types in your account. It will be the same as if the contact went to your email subscription preferences page and opted out of all email.
If you have any questions on this, please reach out to the Community.