Postfix masquerading or changing outgoing SMTP email or mail address

[daniele]

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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

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 # vi /etc/postfix/main.cf

Append following parameter

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 smtp_generic_maps = hash:/etc/postfix/generic

Save and close the file. Open /etc/postfix/generic file:

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# vi /etc/postfix/generic

Make sure tom-01@server01.hosting.com change to tom@domain.com

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 tom-01@server01.hosting.com tom@domain.com

Save and close the file. Create or update generic postfix table:

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# postmap /etc/postfix/generic

Restart postfix:

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# /etc/init.d/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.