I want to know how to create and maintain a email service (like gmail or any thing simpler) are there any scripts or any architecture for that..
yeah sure, why don't you google for "gmail clone script" or "hotmail clone script" but don't expect to make money with that as you are too late, people have their email accounts @hotmail and @yahoo more than 10 years, its not easy to change it, they are addicted as their all contacts are there
If you're looking for a solution for your company or group of friends, try Google Apps. There's a free version available (limited in the amount of users.)