You may be confusing your email client with your email provider. Your client is like your TV. You use the client to view your email just like you use your TV to view your channels.
Your email provider is the “channel.” Some providers are both, such as Gmail and Yahoo! if you normally view them on the web. You can use your client (Outlook, Thunderbird, Apple Mail, etc.) to view any email provider (channel) in the world.
The links that say I Use Google Apps or I use Yahoo! Business Email on the sign up page sometimes cause confusion.
Sometimes users use Gmail or Yahoo! as their email service providers for custom or personal domains, and we provide those users with the links to correct us in instances when we didn’t guess that.
If you don’t use Yahoo! or Gmail as your email provider, simply enter your mail server settings.
Please create a Support request if you need any further assistance with your sign up process.