[kwlug-disc] Self-hosted email leaks home IP address

[Ron]

Anyone running Postfix to self-host email and notice that their home IP 
address is leaked in the first "Received: from" header?


If you haven't noticed, send yourself a message and check if it's happening.


If you have noticed, do you care? What have you done to prevent it?



If you don't self-host, are you still leaking your home IP? Gmail seems 
to remove this first header, so in some sense more privacy via Gmail 
than self-hosting.



I've got a temp work-around via header_checks:


`apt install postfix-pcre`

main.cf:
--------
header_checks = /etc/postfix/header_checks.pcre

/etc/postfix/header_checks.pcre:
--------------------------------
## WORKS for some messages, not all (this one has ?? delimters - telnet?):
/^(Received: from ).*\([0-9\.\-]+cable.teksavvy.com.*\)(.*by .*) from .* 
(.*)$/AU  REPLACE ${1}***ISP name hidden*** ${2} ${3}

/^(Received: from ).*\([0-9\.\-]+cable.teksavvy.com.*\)(.*by .*)$/AU 
REPLACE ${1}***ISP name hidden*** ${2}



NOTE: for testing header_checks.pcre, postmap does *not* create a DB and 
will throw an error if trying to do that like one does with a hash map.

Just test by copying an offending header to a script and run it with:

postmap -vq "Received: from ..."


And the output (of mine) should show:
REPLACE Received: from ***ISP name hidden*** ??by mail.bclug.ca 
(Postfix) with SMTP id 09F5081D15??for <cc at bclug.ca>; Sat,  7 Mar 2026 
20:39:30 -0500 (EST) from=<canto_telnet at maow.net> to=<cc at bclug.ca> 
proto=SMTP helo=<bclug.ca>


NOTE: Thunderbird can be configured to set the elho to 
ehlo.thunderbird.net, which Android client does by default, I believe.


https://support.mozilla.org/en-US/kb/thunderbird-smtp-ehlo

In the config editor, add or change this key:

mail.smtpserver.default.hello_argument

to value:

ehlo.thunderbird.net