I have a web site for one of my jazz groups, and it has a Contact page where you can send us a message and optionally sign up for our mailing list. Over the last few months I have gotten maybe four spammy messages. But there have been about 60 entries where they don’t leave a message but sign up for the list. I sent emails to them all today and they came back with “no such account” bounces. They all had names with corresponding email addresses with a number, like Caitlin De Garis caitlin.degaris20@outlook.com. (This is a fake name and non-existing email so I am not invading anyone’s privacy here.)
Why would anyone do that? I assume it’s a bot but I can’t see any advantage in signing up for a mailing list with a fake email address.