need help with postfix and network email

[tim@atomstrahl.de]

Hello debian-user,

  i setuped a mailsrerver with postfix. i fetch emails fetchmail, get
  them to the clients pc with qpopper and relay them with postfix.

  i am on dialup and my nonexisting domain (workgroup) is
  "atomstrahl.farm", while the real domain where i fetch(mail) my mails from
  is "atomstrahl.de". i setuped a sender_canonical to have the real
  domain in the email-header, the problem i have now is when i send the
  an email to my romeneighbor i have to use as the email adress
  jimmi@atomstrahl.farm (the unreal one) if i use the real
  jimmi@atomstrahl.de it will relayed to the smtp-server in the
  internet.
  basically how can i prevent that emails for local users gets over
  the internet without using the faked email adress?

thanks in advance

-- 
Best regards,
 tim                          mailto:tim@atomstrahl.de