I can confirm that Marketo does employ the List-Unsubscribe header for email sent from our network.
The List-unsubscribe header is text located within an email header, generally unseen by the recipient, that email senders can include to provide a safe way to safely unsubscribe. Over the years email recipients have been trained to not trust links in unfamiliar email, this makes someone less willing to unsubscribe from commercial email and instead they are more likely to complain. By leveraging the List-unsubscribe header this allows the email provider, like Gmail or Outlook.com, to display a trusted Unsubscribe link for email recipients to use. This benefits senders by keeping complaint rates lower.
Marketo uses the mailto: functionality required by Outlook.com and also used by Gmail/Google.
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https://blog.returnpath.com/evolution-of-list-unsubscribe/
Kiersti Esparza
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