please "lead" me into basic mailservice

[tim@atomstrahl.de]

Hello debian-users,

  i have a small LAN with 3WS and 1 ROUTER connected to the
  internet(ISDN). on the router i run debian potato and on the WS
  basically windows.

                 --------------
                    internet
                 --------------
                       |
                       |
                       |
                ---------------
            router with mailserver
                ---------------
                       |
                       |
            ----------HUB---------------------
             |             |               |
             |             |               |
        ----------      ----------      ---------
        client A        client B        client C



  the mailsetup i want on the router fetches all mails from different
  POP3 accounts. the same with SMTP.  the email-clients on the WS
  connects to the mailserver on the router (send and get). Also it
  schould be possible to send mails from client A to client B (C).


  I am confused about this, i installed postfix but i read
  something about procmail, fetchmail. do i need them all ?

  do i need a program that fetches (fetchmail) and drops (procmail?)
  and serve (postfix) the mails?

  as you see i have no clue where to start, i appreciate any input


  thanks  in advance
-- 
Best regards,
 tim                          mailto:tim@atomstrahl.de