The key differences between the Mail From (MFrom) address and the From address include:
- The sending domain of the From address might not be the same as the Mail From (MFrom) domain depending on your sending practices.
- During authentication, Sender Policy Framework (SPF) checks the domain in the MFrom address, not the From address domain.
- The MFrom address is where SMTP error messages (bounce messages) are sent.
- Both addresses can be found in separate locations in the email header, as shown in an example below.
The MFrom address is also referred to as the Return-Path address, Envelope-Sender address, and the bounce address.
X-Apparently-To: firstname.lastname@example.org; Wed, 20 Jan 2016 11:11:10 +0000
Received-SPF: pass (domain of returnpath.net designates 126.96.36.199 as permitted sender)
Content-Type: text/html; charset=utf-8
X-Mailer: MIME::Lite 3.027 (F2.74; A2.03; B3.07; Q3.07)
Date: Wed, 20 Jan 2016 04:11:09 -0700
From: Return Path Monitor <email@example.com>
Reply-To: Return Path Monitor <firstname.lastname@example.org>
Subject: Here's why your mail is getting filtered...
X-Rptags: Newsletter 1453288262