so go out and learn something about it rather than wait for people to do your work for you...
I'm pretty sure that a quick adventure with your favourite search engine would yield a wealth of information.
and we're not able to handhold you all the way. We can help you with specific point problems, maybe turn you in the right direction for broader decisions, but that's as far as we can usually go.
Without knowing what you know, it's impossible to even start.
Should we start pointing you to an introductory text on C++ programming or an advanced text on network protocols for example?
Both are relevant to writing a mail program (and do you want a server or a client?), which you should read depends on what you know already.