MailUp is an email service provider (ESP) based in Italy, with a worldwide customer base. Here is an example of a default MailUp configuration with the List-Unsubscribe header. MailUp implemented this header since the new version 6.0. This header is by default added to each email message sent by our customers. Only MailUp resellers can customize it. The link provides a one-click unsubscribe: the email is saved in a "blacklist": this means that the sender will not be able to send anything more, even if he imports a new email list.
From: Paola Anni <email@example.com>
To: "firstname.lastname@example.org" <email@example.com>
Content-Type: text/html; charset=ISO-8859-1
X-Abuse: Please report abuse here: http://www.mailup.it/email-marketing/Policy-antispam_ENG.asp