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

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: "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!" I'm the only person using my domain name, haha.