I have developed a WEB application for my company. All users access it via intranet. How can I configure a SMTP server to use only the intranet, since we don't have internet access in the company, thank you for you support.
Setting up a mail server is a complex task. It depends on your server os and your requirements. There are many tutorials on the internet.
Example mail servers on Linux are Postfix or Exim. On Windows you can try Mercury. Mercury is also shipped with XAMPP.
I've used postfix for sending mail on a local network and dovecot to provide POP and IMAP mail collection.
You don't need to have a real domain name to set this up.
There are lots of HOWTOs that can show you how to set them up: