Emails sent by Early Bird to a user in response to an action by that user are called transactional emails. An example is an email sent when a user requests an email login link. Emails sent for other reasons, such as to invite guests to an event, are technically referred to as marketing emails, even if there's nothing very marketing-ish about them. When Early Bird sends a marketing email, the email always includes a one-click unsubscribe link, which means the user doesn't need to click anything else to unsubscribe.
When a user unsubscribes by clicking an unsubscribe link, they are unsubscribing from the specific event. They can still receive "marketing" emails from other events, and transactional emails. If they want to resubscribe, they can do so on their RSVP page. The host can also do that for the guest.
After the users clicks the unsubscribe link, Early Bird displays the unsubscribe page. On that page the user may elect to unsubscribe from all events hosted by a specific host. The enables users to avoid being annoyed by specific hosts. The host cannot resubscribe the user. The user can resubscribe from their settings page, which is accessed by clicking the avatar icon on the top right of all pages once logged in. For privacy reasons, the host will not be aware that the user has unsubscribed.
On the unsubscribe page, users may unsubscribe from all Early Bird event email. This can be reversed only by the Early Bird support team. For privacy reasons, the hosts will not be aware that the user has unsubscribed.