need knowledge regarding SMTP server

one of my friend built a website that can offer website users to use our server to send email to their business peoples. we want to provide users following information

a sign up form to create an id in our site and use registered username and password in the information below.

SMTP SERVER : ourserver.smtp.com
SMTP PORT : 25
Username : registeredUsername
Password : registeredPassword

and user enter these information into their email sending software to send emails from our server.

What we require to achieve this task?

Hmm...I'm a little confused. Do you guys want to create your own mail server like gmail or hotmail ? Or is there something more ?

yes own email service like hotmail, gmail and yahoo

Then you need to know how to implement the SMTP protocol.

Here is a page where a simple SMTP server is partially implemented in VB.Net. There is also a link there that leads to a document that describes the SMTP protocol, so you should be able to do a complete implementation yourself.

EDIT

While the SMTP docs can tell you everything you need to know to create one, I'd advise that you first look for one that's already implemented. Perhaps an open source implementation that's made to be used by other developers. The reason I suggest this is because creating a complete implementation may in itself be a full time project by itself not something you can just throw together in a couple of days. If you're willing to put in the time then by all means go for it, if not, look up one.

thank you very much.
i will check it all