A donor or constituent can unsubscribe from all future emails by clicking the unsubscribe link at the bottom of your email marketing messages.  A constituent can also manage their own subscriptions via the Donor Portal. The constituent would log into their portal account and can find the link to manage their subscriptions under their name in the top right corner.  From the Email Subscriptions page, they can select or unselect email list categories, not specific email lists.  They could also check the box "Unsubscribe from all" to be removed from all future email campaigns.