How to rewrite outgoing address in Postfix

Postfix masquerading or changing outgoing SMTP email or mail address

Sometimes I find myself configuring an internal Linux machine to be able to send emails for alerts or from a particular application. Since this will not be a primary mail server, I just want to rewrite the outgoing address to be something that make sense with the proper domain for the users. Here are the quick steps to accomplish this:

Tested with "postfix-2.3.3-7.el5"

vi /etc/postfix/

Modify the "mydomain" variable to your email domain
mydomain =

Make sure to uncomment the proper network interface
inet_interfaces = all

Now at the bottom of this file you need to specify the generic map file for rewriting the address.
smtp_generic_maps = hash:/etc/postfix/generic

Save and exit Now we need to edit /etc/postfix/generic

vi /etc/postfix/generic

You need to specify the mapping of the original address to the one you want. Since in this case I just want to rewrite everything I usually add the following two lines and it seems to catch everything.

Save and exit the file. Now we need to create the postfix db.

postmap /etc/postfix/generic

This will create the /etc/postfix/generic.db hash file.
Now just restart postfix and test.

/etc/init.d/postfix restart

For Older version

EDIT: so I was doing this on an old version of Red Hat/Postfix 2.0 and my own directions didn't work. (embarrassing...) Turns out you have to use a different file. Instead of using smtp_generic_maps, use sender_canonical_maps like so:

sender_canonical_maps = hash:/etc/postfix/canonical

Then /etc/postfix/canonical is setup just like the generic file example above. Use the

postmap /etc/postfix/canonical

Restart postfix and test.