I got a very similar email last year. This isn't new and I think they're just blindly sending emails to anyone with a custom domain name. Got one from Katy last year thanking me and saying:<p>"You may not be aware, but many of your colleagues are also using Dropbox for their work. It’s great to see this high level of engagement!"<p>I'm the only person using my domain name, haha.
I don't know how these are sleaze emails. These are marketing emails. If you are using a free version of something, they will try to push you to a paid or enterprise version. I bought an iPhone but still get emails from them to get the Apple TV or the Apple News or the Apple Card service. How is this any different.