Quote:How do I start coding an email services, like yahoo, gmail, zoho mail?
The way the question is worded, you have same chances to fulfill the project if you had asked: I did directions to start building a space shuttle in my backyard, on budget.
Those services are incredibly complicated, they have required hundreds of years of seasoned engineers/programmers. If there is not thousands of such services, there are reasons.
Advice: Redefine your project, list functionalities you want, study each of them, try to find open source projects, play with them, have a look a source code.