After you've created a new email address in the Control Panel (see FAQ "Adding more email addresses to your account") you can access your email account on the web by typing "webmail" after your URL like this:
"www.yoursite.com.au/webmail"
Put in your full email address as your username (you@yoursite.com.au) and then your password. And then follow the prompts to get to your inbox.
Even if you've set up your email address to work with Outlook Express the above is useful to know. If, for example, you delete an email by accident from Outlook Express you can still retrieve it directly from the server by going to Webmail.