Yes!
To ensure uniqueness, and to avoid confusion about redirections and weird numbered usernames, Mr.Host has designed a system to allow you to login directly as your e-mail address.
This system allows us to keep our accounts unique on our mail system side, but still allows you to have any e-mail address you’d like at your domain.
This also means you only have to remember your e-mail address and password, not some other confusing login account name.