Maybe if you email cold prospects. With tracking links. And hidden tracking images. And automate sending it every week. And make the email sound increasingly urgent. And call them something intriguing like 'drip campaigns'. And include no unsubscribe link.
We could even build a service to do all of that. I suggest calling it spam.io
"Oh but you're not subscribed to anything. These are just individually sent emails from someone directly connecting with you. On a schedule. That all look the same. And are the same for every person its sent to with the name of the business filled in." wink wink nudge nudge
This varies by country, but for the United States, the law requires you to honor opt out requests. A link is one mechanism to honor such a request. Another way is to remove a recipient from a list after they reply stating their wish to be unsubscribed.
From a practical level, it is worth including an unsubscribe link just to avoid having someone mark your email as spam after not being able to find the unsubscribe link.
We could even build a service to do all of that. I suggest calling it spam.io