How can I configure Postfix to silently drop / discard mails that were sent from one of my users to an external address?

I'm already able to discard all mails to external addresses using the following transport_maps

example.com      :
*          discard:

However I want to apply this rule to one user within my Postfix server only.

Also mails addressed to external and local addresses should get deliverd to the local users only.

Why do I need this?

The company I work at thinks that an intern should not sent mails directly to the customer. So the intern would send a mail using the customers address for to and adding his supervisor into the cc. Then Postfix shoud only deliver the mail to the supervisor so that he can check and sent the mail to the customer without searching for the customers address.

2 Answers 2


To do what OP need, we need a check at transport level, which turn out to be simple.

  1. Add following line to /etc/postfix/main.cf

    sender_dependent_default_transport_maps = hash:/etc/postfix/sender_transport_maps
  2. Create /etc/postfix/sender_transport_maps as follow

    [email protected]   discard
  3. Create postfix map file and restart postfix

    cd /etc/postfix
    postmap sender_transport_maps
    service postfix restart

This method works because postfix only use transport map for out-bound mail. In this case, instead of using a normal smtp service (smtp:), we use postfix DISCARD service.

  • This just discards all mails from that sender - but I want to discard external mails only (mails not ending with @example.com)
    – Martin
    Dec 16, 2012 at 22:54
  • So you want a specific user's email to a specific address be discarded?
    – John Siu
    Dec 16, 2012 at 23:02
  • Almost. I want a specific users's mails to be send to the local addresses only - external mails from this user should be discarded silently.
    – Martin
    Dec 16, 2012 at 23:42
  • ok, i have to revise the answer later. I am outside now and this is soemthing you don't keep in your head, lol.
    – John Siu
    Dec 16, 2012 at 23:46
  • no problem - and thank you for helping me!
    – Martin
    Dec 16, 2012 at 23:51

The sender_dependent_default_transport_maps didn't work at all for me. Even with smtpd -vv in master.cf to increase debug didn't help let me know why it didn't work (possibly an old postfix version).

Instead I used

smtpd_sender_restrictions = check_sender_access  pcre:/etc/postfix/sender_domains, discard

with the sender_domains file containing

/[email protected]/  DISCARD
/@domain.com/ OK

for eg, then restart postfix (pcre files do not need to be/can't be postmap'd)

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