Yes, emails are hosted on a separate infrastructure. Hosted.com's WordPress Hosting servers are specifically configured (both hardware and software) to ensure maximum speed, security, and optimal performance, for your WordPress website. The email environment has changed dramatically over the past years, as more and more people access their emails across multiple devices. This means that they are not downloading them from the server, which in turn creates an additional load on hosting servers. Hosted.com has created a separate email server platform for WordPress clients so as to avoid this additional load from impacting their WordPress websites' loading speeds.
Read more in our Article: WordPress Email and Hosting: Integration and Options.