Depending on the software you are using, you may need to change the outbound (from) address of outbound email.  In this How-To, we will change the outbound email address from “apache@example.com” to “webmaster@example.com”.

To start out, go to your postfix directory and modify/create your generic file.  Your generic file will map the two addresses to each other.  At the end of your generic file add a space or tab seperated file simmiler to this.

apache@example.com         webmaster@example.com

Once you have added the entries to your generic file, you need to hash the file so postfix may quickly access it.

postmap /etc/postfix/generic

After you map has been created, you will need to add the entry to your main.cf file to tell Postfix to use your generic map.

smtp_generic_maps = hash:/etc/postfix/generic

Once you have updated your main.cf file, you need to reload postfix

postfix reload