Also, a lot of companies nowadays keep adding weird email topics that you need to constantly unsubscribe from.
If I signed up and turned off all subscriptions, then anything they send is marked as spam immediately. The lack of cost in sending email makes it easy for them to keep abusing all the time.
Mark it as such.
And, as others have noted, unsubscribe cannot involving going and logging into their system. If I need to do that, it generally goes directly to spam.
My gut says unsolicited marketing emails, from popular sites I've never used before, like Brooks Brothers or Robinhood (especially after a "Welcome to ${site}!") or US public school event notification emails are all probably legit mistakes.
I could see even a public school system having issues with getting flagged as spam if they don't include an easy method to unsubscribe because then marking as spam+blocking becomes the best option in response to wrong address.
Which of course you click and then have to go through a number of hoops to log in, confirm Email address, authenticate, etc.
At this point, I just mark those as spam as well.
I've noticed a recent trend where unsubscribing actually does nothing