List-Unsubscribe header

What is the "List-Unsubscribe" email header?

This is an optional string of text that email you can add to the header area of your emails to make it easy for email providers and email clients to handle unsubscribes.

We recently covered how Gmail uses this header in a blog post:

Apparently Outlook also uses it to display a high-visibility "Unsubscribe" button.

Why is it important?

The easier it is for your email recipients to unsubscribe from your lists, the less Spam complaints you'll receive, and the higher your Sender Score (email reputation) will be.

How do I set it up?

In whichever system or software you use to send messages to your subscribers, you need to edit its email header area and include a new field:

List-Unsubscribe: <>, <>

Note that it supports both a web-based (http) and an email-based (mailto) mechanism.

How can I test that it's setup properly?

The "List-Unsubscribe" header is one of many things that are validated by the Winning Email domain checkup tool: