I would recommend reviewing some of the how-to's for your project. there are several sites that have complete walk-thru instructions on how to configure a mail server using postfix and Dovecot, (or Courier / Cyrus for IMAP ond POP3 functionality depending on your needs)
Mr. C is correct you should define your needs first.
Do you want just a basic mail server ?
Do you want the server to block SPAM (Spam assassin / Dspam) ?
Do you want to Scan mail for viruses (ClamAV) ?
Do you plan on hosting more than one domain on a single server (virtual domains) ?
Do you want Webmail access (Squirrel webmail / Other) ?
After you determine what you need there are a lot of resources available.
That's a start.
When following the how-to's they typically have steps in them to TEST the system as you progress, to ensure things are working properly thus far. do not skip those steps, or keep moving forward until the tests are successful.