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

[Chris Irwin]

On Tue, Mar 10, 2026 at 01:00:14PM -0700, Ron wrote:
>
>Anyone running Postfix to self-host email and notice that their home 
>IP address is leaked in the first "Received: from" header?

Question: What is your mail setup?

I'm assuming:

1. Self-hosted SMTP on "cloud" somewhere, with a public IP address

    That SMTP server is public, it's IP is your domain's mx server, etc.

2. You as a client, sending outbound via (presumably authenticated) SMTP

    Your public SMTP server does the "normal" thing of adding a 
    "received" header

In this case, most hosted mail solutions don't do the "received" header 
for authenticated outbound user mail. Gmail (as you tested) or fastmail 
(which I tested), and presumably everything else.

>If you don't self-host, are you still leaking your home IP?

I'm leaking via DNS all over the place. But I'm not self-hosting mail 
anymore, so technically "no" for that.

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

Also, does this only act on mail you're sending? Or will mail you're 
receiving be similarly altered?

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

Why not an IGNORE rule to just drop that record entirely?

-- 
Chris Irwin

email:   chris at chrisirwin.ca
   web: https://chrisirwin.ca