I may have read the post wrong, but if you are looking to offer free email addresses to your users, you may want to take a look at HiveMail... To set it up with cpanel, you just need to set your catch-all email address and pipe it to the hivemail script. Anyway, full instructions are included with HiveMail.
Do read your hosting provider TOS if you plan to host the email service on a shared environment. Most hosting provider would state under their TOS banning you from running form of free service like free webhosting or in your case free webmail.
By signing up for Windows Live, you will get a new e-mail account @mygsp.com. Your e-mail account will be provided by MSN Hotmail, a leading provider of free webmail. Your e-mail address is your Windows Live ID, which can also be used to access instant messaging and other services on the MSN and Windows Live network
Show your reciprocal links on your website. eReferrer