Postfix masquerading or changing outgoing SMTP email or mail address

last updated in Categories Debian Linux, Gentoo Linux, Linux, Mail server, Postfix, RedHat/Fedora Linux, Suse Linux, Ubuntu Linux, UNIX

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

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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
# vi /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:
# /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.

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Posted by: Vivek Gite

The author is the creator of nixCraft and a seasoned sysadmin, DevOps engineer, and a trainer for the Linux operating system/Unix shell scripting. Get the latest tutorials on SysAdmin, Linux/Unix and open source topics via RSS/XML feed or weekly email newsletter.

16 comment

  3. Thanks this was helpful. I needed to be able to get my home server to forward mdadm alerts to my external email address through my isp’s smtp server (cox cable) and this was the missing piece.

  4. I get this strange message from smtp.com in /var/spool/postfix/defer
    I have found this message
    for EVERY mail attempted sent via Postfix:

    : host smtp.com.inbound10.mxlogic.net[208.65.144.3] said: 451
    Could not load DRD for domain (1base.com) rcpt (eo@1base.com) (in reply to
    RCPT TO command)
    recipient=eo@1base.com
    offset=133
    status=4.0.0
    action=delayed
    reason=host smtp.com.inbound10.mxlogic.net[208.65.144.3] said: 451 Could not
    load DRD for domain (1base.com) rcpt (eo@1base.com) (in reply to RCPT TO
    command)

  5. Thanks this was helpful. I needed to be able to get my home server to forward mdadm alerts to my external email address through my isp’s smtp server

  7. Hey Vivek,

    I would like something similar done, but only for one email address and not all the emails being sent out.

    Any ideas?

  8. This was a big help, thank you!

    Gagan, those instructions work for just one email (that was all I needed to do too.

  9. Worked great – it’s now sending mail from the correct address. But postfix says my name is ‘root’ – any easy way to change that?

  10. hi,
    i am using postfix and currently i can use any email address to specify FROM id.
    so it is like faking any email address. smtp use can change his/her from email address. so i was wanting to change the from email address to the one with the same username.
    for example: user live can send email from herry@domain.com but i want to restrict all user to use there own email address and own domains.
    i want to restrict user live to send mail only from live@domain.com not any other like anyuser@anydomain.com
    any help will highly be appreciated
    greeting from Nepal,
    ~prahmod

  12. Hi, I liked your article but don’t know exactly if my question is answered by your article. Actually I receive email from a particular domain where they change the source domain in email to my domain (for example abc@source-domain.com is changed to abc@receiver-domain.com) On reading complete headers the real domain is revealed but in From: header they put a fake address as abc@recevier-domain.com, where receiver-domain is my domain. How they do it? Is it legal and if so then what is the purpose?

  13. @alice that is actually illegal but one can easy forge their domain and use any domain name if they own a mail server…Generally these type of activities are done by spammers to spam and sometime even by attackers to create a certain email to seem like a mail originating from the legitimate domain..
    To control this type of forgery one can use dns service to update their SPF. https://en.wikipedia.org/wiki/Sender_Policy_Framework
    so that email originating from a particular ip are treated as genuine and other then that ip with that domain name as spam..
    Google, yahoo and other mail provider use this technique to know that email are send from the allowed ip or not

  14. Thanks for a great post on Postfix masquerading or changing outgoing SMTP email or mail address. This is very helpful for a newbie like me.

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