#Postfix masquerading or changing outgoing SMTP email or mail address via http://www.cyberciti.biz/tips/howto-postfix-masquerade-change-email-mail-address.html
Address rewriting allows changing outgoing email ID or domain name itself. This is good for hiding internal user names. For example: SMTP user: tom-01 EMAIL ID: [email protected] Server name: server01.hosting.com
However when tom-01 send an email from shell prompt or using php it looks like it was send from [email protected]