It is a legal requirement to allow users to unsubscribe from your email newsletter, yes. What Slack does that is really cool is at the bottom of their notifications email they have:
Snooze these notifications for: an hour, eight hours, a day, three days, or the next week. Or, turn email notifications off. For more detailed preferences, see your account page.
"hour", "eight hours", "three days", "next week" are all links that silence the notifications for discrete periods of time. Pretty neat.
It's not just unsubscribe. They let you turn off emails for an hour, a day, etc. Really convenient if you're generally interested in notifications, but just need a little break.
Another example: when you change your password, Slack will send you a special link to sign-in on mobile so you don't have to type out your new password on a tiny keyboard.
Snooze these notifications for: an hour, eight hours, a day, three days, or the next week. Or, turn email notifications off. For more detailed preferences, see your account page.
"hour", "eight hours", "three days", "next week" are all links that silence the notifications for discrete periods of time. Pretty neat.