#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: tom@domain.com 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 tom-01@server01.hosting.com
In some cases internal hosts have no valid Internet domain name, and instead use a name such as localdomain.local or something else. This can be a problem when you want to send mail over the Internet, because many mail servers reject mail addresses with invalid domain names to avoid spam.
Postfix MTA offers smtp_generic_maps parameter. You can specify lookup tables that replace local mail addresses by valid Internet addresses when mail leaves the machine via SMTP.
Open your main.cf file
vim /etc/postfix/main.cf
Append following parameter
smtp_generic_maps = hash:/etc/postfix/generic
Save and close the file. Open /etc/postfix/generic file:
vi /etc/postfix/generic
Make sure tom-01@server01.hosting.com change to tom@domain.com tom-01@server01.hosting.com tom@domain.com
Save and close the file. Create or update generic postfix table:
postmap /etc/postfix/generic
Restart postfix:
service postfix restart
When mail is sent to a remote host via SMTP this replaces tom-01@server01.hosting.com by tom@domain.com mail address. You can use this trick to replace address with your ISP address if you are connected via local SMTP.