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Summary

The common confusion surrounding SPF (Sender Policy Framework) checks often revolves around which domain is actually validated. Many assume it checks the 'From' header address, but the standard protocol specifies that SPF primarily authenticates against the Return-Path domain, also known as the Mail From domain or envelope sender. Understanding this distinction is crucial for proper email authentication and deliverability, especially when using third-party sending services or subdomains.

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What email marketers say

Email marketers often wrestle with the nuances of SPF, particularly when using external sending platforms. There's a persistent belief that SPF should validate the 'From' header domain, but experienced marketers emphasize that the Return-Path (or Mail From) domain is the critical point of inspection. This misunderstanding can lead to incorrect SPF configurations, potentially affecting email deliverability and even causing blocklist issues.

Marketer view

Email marketer from Email Geeks clarified that SPF strictly checks against the Return-Path domain. They emphasized that if a third-party platform uses its own Return-Path for bounce handling, adding their details to your domain's SPF record would be ineffective and unnecessary for authentication.

03 Dec 2020 - Email Geeks

Marketer view

Email marketer from Email Geeks highlighted a common misinterpretation in third-party authentication guides. These often mislead users into believing they need to include every sending platform in their primary domain's SPF record, which can inadvertently cause them to exceed the 10 DNS lookup limit, leading to authentication failures.

03 Dec 2020 - Email Geeks

What the experts say

Industry experts provide clarity on SPF's authentication mechanisms, debunking common myths and offering practical advice. They emphasize that while the SPF protocol primarily checks the Return-Path domain (5321.from), historical practices and specific receiver implementations (like Microsoft's past behavior) sometimes led to confusion regarding the 'From' header (5322.from). Experts advise careful configuration to optimize deliverability and avoid exceeding DNS lookup limits.

Expert view

Expert from Email Geeks states that the SPF protocol explicitly directs SPF checks to the 5321.from domain. They add that in cases where mail has a null sender, the SPF check is performed against the HELO/EHLO value.

04 Dec 2020 - Email Geeks

Expert view

Expert from Email Geeks recalled previous discussions about Microsoft's historical SPF checking behavior. They mentioned that in the past, Microsoft sometimes checked against the 5322.from domain, which led to recommendations for SPF publishing in both the 5321.from and 5322.from domains.

04 Dec 2020 - Email Geeks

What the documentation says

Technical documentation consistently clarifies that SPF checks are performed against the domain specified in the RFC 5321 Mail From address (the Return-Path). This contrasts with the RFC 5322 From header, which is the 'friendly' address seen by recipients. Adhering to these specifications is vital for effective email authentication and for preventing your legitimate emails from being flagged as spam or outright blocked. Understanding this distinction is fundamental for anyone managing email infrastructure.

Technical article

Documentation from DuoCircle specifies that an SPF record is a straightforward text record. Its primary function is to list all authorized hostnames and IP addresses that have permission to send emails on behalf of an organization's domain.

15 Oct 2021 - DuoCircle

Technical article

Documentation from IONOS Digital Guide states that SPF, or Sender Policy Framework, is a crucial method. It enables mail servers to verify whether a received email genuinely originated from the specified host server, thereby enhancing email security.

20 May 2023 - IONOS Digital Guide

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