A webmail feature accessible from your browser address bar:
Linux shared server plans user:
http://webmail.yourdomain.com/ (or http://www.yourdomain.com/webmail/)
Windows shared server plans user:
http://mail.yourdomain.com/
(substituting yourdomain.com with your actual domain name), in the Email Address field, type in the email address of the mailbox that you are checking.
Please note, if you are using an email address that forwards to a mailbox, you will need to type in the name of that mailbox, and not the forwarding email address. In the Password field, type the password for the mailbox that you are checking. You will then be taken to your Webmail folders, where you can check your inbox, compose a new message, etc.