To check your webmail, simply use the URL: http://webmail.yourdomain.com/ where "yourdomain.com" is the name of your domain.
Under "Email-Utilities:" select "IMP-mail client" and login with your full email address as your username (user@domain), and of course your password...
or
Go to Sustainable Hosting's Webmail page and login with your full email address as your username (user@domain) and of course your password...