How do I set up postfix to store e-mail in a file instead of relaying it?

I created a new transport with a pipe command that writes e-mail down to a file.

Basically:

1. Create a user that will own e-mail (or use an existing one). I called mine email
2. mkdir /home/email/bin

3. Place the following script in /home/email/bin/mail_eater (this uses PHP, but you can write your own version in any language you like, it just appends stdin to a file):

   #!/usr/bin/php
   <?php
   $fd = fopen("php://stdin", "r");
   $email = "";
   while (!feof($fd)) {
       $email .= fread($fd, 1024);
   }
   fclose($fd);
   $fh = fopen('/home/email/email.txt','a');
   fwrite($fh, $email."\n-------------------------------------------------------\n\n");
   fclose($fh);
   

4. chmod a+x /home/email/bin/mail_eater
5. touch /home/email/email.txt
6. chmod a+r /home/email/email.txt

7. Create a new transport using this file by appending the following line in master.cf:

   file_route unix -    n    n    -    -    pipe user=email  argv=/home/email/bin/mail_eater
   

8. Use this as the default transport in main.cf:

   default_transport = file_route
   

There :)

You could put those domains into $mydestination in main.cf, so postfix will deliver it locally.

You can set up different local users if you want or you can setup a local catch-all address to deliver emails into just one account, more details here: http://www.postfix.org/ADDRESS_REWRITING_README.html#luser_relay

For all domains:

mydestination = pcre:/etc/postfix/mydestinations

and /etc/postfix/mydestinations should contain

/.*/    ACCEPT

I cannot test right now but it should work.