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?