List-Unsubscribe is an optional email header that allows email recipients to opt-out of receiving emails without clicking through an unsubscribe link or marking a sender as spam or junk.

It is displayed next to the email sender information.

List-Unsubscribe Header is a user-friendly way to offer an opt-out for your recipient. Thus, they won't have to search for a unsubscribe link in your email body.

Offering such feature in your emails is a good way to avoid that your recipients mark your email as spam to not hear from you again. Which is very damageable to your email deliverability.

Find out How to setup a List-Unsubscribe Header for your emails