I received an email about threads and Mastadon a bit ago. The thing is I deleted my Mastadon account a hot minute after I created it. The email has no way to unsubscribe from it 
I would like to be comforted that I’m overthinking this. My Mastadon account was a couple of years ago in both creation and deletion. It’s incredibly disconcerting.
That e-mail isn’t from Mastodon, it’s from SDF.org. It relates to their Mastodon instance - and Mastodon in general - but it’s specifically an update relating to the service they offer.
Might want to check to see if you have an account there.