Log in
Use the same password as in cPanel. Passwords are changed in cPanel, not here.
Mail for your hosting account
This server carries the email of your cPanel hosting account: it receives mail for your domains and sends your mail on to the world, within the account's hourly limit.
Webmail
Read the last two weeks of your mail, and the mail you sent, from anywhere.
Mail trace
Follow a message: when it arrived, where it went, or why it bounced.
Sending limits
If an email address sends too much, or too much of its mail bounces, its outgoing mail is halted for a while, and you are told why. Other addresses are not affected.