A Recap About List-unsubscribe

Service Pack 20 saw the inclusion of a list-unsubscribe header on all your outgoing emails. This an industry standard feature favored by inbox providers such Gmail, Outlook, iOS and others. It is a simple “Unsubscribe” link in the header of an email that allows recipients to opt out rather than hit the “spam” button if they don’t want to get an organization’s emails.
You don't need to do anything to enable or configure this. The header will automatically be added to emails by inbox providers that support it.
This functionality was added to Blackbaud Internet Solutions some time ago and is referenced in the New Features Guide. It resulted in reduced spam complaints where we saw a measurable boost in sender reputation and improved inbox placement for our customers. Inbox placement rate immediately went up and resulted in fewer spam complaints. Only small fraction of email recipients - less than 1% - used the list-unsubscribe header to opt out.

This is not a replacement for standard unsubscribe functionality. You should continue to include an easily visible email unsubscribe link in your email message body to make it easier for individuals to indicate their message preferences.

Remember, faster unsubscribes equal fewer spam complaints.
For more information about Email Best Practices see our Email Resource Center