Hi !

Coupons are special text string , they have two types , Paid and trail .
you can generate the coupuns  of any type you want and then allows user to sign up for an email address  and use the coupons you gave them to get an account . this is good way let users test the web mail application for soem days and when they satisfied or there trail has ended then they can pay  to continue with web mail system   

User can sign up  with folling options  that you can set via admin panel

1 - Free account
2 - Free trail account ( you can set number of days from admin panel )
3 - Coupons accounts ( explained above )
4 - Both types of accounts  ( free account and trail account )
5 - Only paid account ( these show the payment options you set via paymnet gatways )  

Thanks
Suhail kalem
mailyoulike.com