Just a short overview of the Postfix mailing system

• Clients mount the "maildrop" directory from the file sever and do not have to runs any resident Postfix processes at all.
• Postfix has four different queues:maildrop,incoming, active and deferred. Actually five if we count the mailbox directory as a kind of queue (mails wait there to be readed).
• The Postfix master daemon runs the following programs (on request):
  sendmail (same name but not to be confused with the "old" sendmail!)
  pickup (read the maildrop queue and pass the mail to the cleanup program)
  cleanup (got mail from different daemons and put it into the incoming queue)
  smtpd (get mail from Internet and pass it to the cleanup program)
  smtp (called by the queue manager to send mail to Internet)
  qmgr (core program: read from "incoming", put into "active" and call an appropriate "delivery agent")
  resolve
  local
  pipe
  rewrite

Click here to see an official picture of the main Postfix system, which is explained in short below:

receiving mail

• local mails, i.e. mails from the mail server itself (i.e. sirius) are written bei der sendmail emulator into the maildrop queue.
• the pickup daemon read from the maildrop queue and put the mails into the incoming queue with the help of the cleanup program.
• local mails from our client Workstations (mail clients) by some "User Agent" [as for instance mailx , mailtool , dtmail , pine , elm] are sent to the mail server (sirius) through the internet using the smtp utility. The smtpd daemon on the server treat them as any external mail.
• external mails from Internet are received by the smtpd daemon and written into the incoming queue with the help of the cleanup program.
• The cleanup program notify the arrival of new mails to the queue_manager program.

  sending mail

  The heart of the Postfix mail system is the queue manager program.
• qmgr basically read mails from the incoming queue and send delivery requests with queue file pathname information to the appropriate daemon (local or smtp or pipe). In doing this it uses a small queue called "active" to avoid problems under haevy load.

Configuration

• file master.cf control the behavior the master daemon.
• file main.cf control the behavior the Postfix mail system.

More information about our local implementation later (hopefully ...)

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