It is so common I'd be surprised if you weren't seeing these login attempts. Every ssh server I've run in the last 10 years has had this happen, even those with

It is so common I'd be surprised if you weren't seeing these login attempts. Every ssh server I've run in the last 10 years has had this happen, even those without domain names. They must just scan random IPv4 addresses for anyone responding on port 22. It's the modern equivalent of wardialing.