HOW TO : Block outbound e-mails in Postfix

I ran into a challenge at work, where we had to allow e-mail delivery for certain domains, but block all other domains. But at the same time, we had to ensure that the clients sending e-mails did not get a delivery error. We were using Postfix as the MTA running on Redhat Linux. Here’s how I resolved it

  • Edit the file (the default location is in /etc/postfix) and add “transport_maps = hash:/etc/postfix/transport” (without the quotes) to the file.
  • Create a file named “transport” in /etc/postfix, if it doesn’t exist
  • Add the following at the end of the transport file

* discard:

  • Run “postmap /etc/transport” to create a hash of the transport file
  • Run “service postfix restart” to restart the postfix service

This configuraiton will ensure that all e-mails address to DOMAIN1 and DOMAIN2 are delivered normally, but the rest of the e-mails are silently discarded.

Note : Ensure that you follow the syntax for where to place the : verbatim.