---
title: "Understanding the concept of fallback mechanisms in Sender Policy Framework | DuoCircle"
description: "Sometimes, when an email doesn’t pass the SPF authentication checks, the receiving server or policies offer better ways to handle or mitigate the failure."
image: "https://www.duocircle.com/images/og-default.png"
canonical: "https://www.duocircle.com/blog/email-security/understanding-the-concept-of-fallback-mechanisms-in-sender-policy-framework/"
---

Quick Answer

SPF fallback mechanisms are the conditions under which an SPF failure does not block a message. The main fallback is DMARC alignment: if SPF fails but DKIM passes with alignment, DMARC passes and the receiver typically delivers the mail. This protects against legitimate forwarding scenarios where the original SPF source is replaced (mailing lists, .forward rules, alumni forwarders). The softfail qualifier \~all is itself a fallback: receivers may accept the message with a spam tag rather than reject it. ARC (Authenticated Received Chain) preserves authentication results across forwarders so downstream receivers can trust the upstream pass. Senders should never rely on fallbacks to mask configuration errors; the goal is hard SPF or DKIM alignment on every legitimate path, with fallbacks covering edge cases like forwarding.

Understanding the concept of fallback mechanisms in Sender Policy Framework

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![mechanisms in Sender Policy Framework](https://media.mailhop.org/duocircle/images/2025/01/spf-record-check-6359.jpg) 

Sometimes, when an email doesn’t pass the [SPF](/resources/what-is-spf) authentication checks, the receiving **server or policies** offer better ways to handle or mitigate the failure. This is done using fallback mechanisms, a way to secure [email communication](https://www.tidio.com/blog/email-communication/) without hampering the flow and productivity. 

These mechanisms prevent phishing and spoofing attacks while ensuring your [email marketing campaigns](https://www.campaignmonitor.com/resources/glossary/email-campaign/) **engagement and conversion rates** don’t take a toll. Let’s understand what these fallback mechanisms are and how you should use them to multiply the efficiency of email communication.

## SPF alignment with DMARC

When an email fails the SPF check but passes the overall DMARC check, the recipient’s mailbox can ignore the SPF result and continue placing the email in the primary inbox. This **fallback mechanism** is especially useful for a domain that is new to [email authentication](/resources/email-authentication) protocols. 

[![Fallback Mechanism](https://media.mailhop.org/duocircle/images/2025/01/sender-policy-framework-12.jpg)](https://media.mailhop.org/duocircle/images/2025/01/sender-policy-framework-12.jpg)

## Soft fail (\~all)

SPF has two failure mechanisms: soft fail and hard fail. Every domain owner or SPF administrator has to choose between one of the mechanisms and mention it in their SPF record so that the **recipient’s server** knows what you want to be done with [illegitimate emails](https://www.linkedin.com/pulse/illegitimate-emails-protect-yourself-indigo-it-limited) sent from your domain. 

SPF soft fail instructs the receiving servers to mark illegitimate emails sent from your [domain as spam](https://thehackernews.com/2024/02/8000-subdomains-of-trusted-brands.html). While this mechanism offers partial protection against potential [phishing emails](https://www.securitymagazine.com/articles/100398-report-over-176-billion-phishing-emails-were-sent-in-2023) sent on your behalf, it doesn’t put communication at risk because of the instances of false positives. Soft fail is usually **used in two conditions**\-

- The domain owner has just started with email authentication protocols and is still in the **testing phase**. This mechanism helps them understand how their emails are performing and if someone is sending out malicious ones on their behalf.
- _Businesses that have low-risk tolerance when it comes to marketing emails_. So, they can’t afford to have genuine emails get rejected because of [false positives](https://www.infosecurity-magazine.com/opinions/false-positives-burn-teams-out/).

## Neutral (?)

This is an optional and least restrictive SPF fallback mechanism. It’s actually a security vulnerability to use the neutral mechanism as it indicates that the domain owner is not asserting if a **specific IP address** is authorized to send emails on their brand’s behalf or not. This lack of guidance leaves recipient [mail servers](https://www.cloudflare.com/learning/email-security/what-is-a-mail-server/) to decide independently, which can lead to inconsistencies in email handling. It undermines the whole purpose of verifying the legitimacy of email senders. 

## SPF hard fail (-all)

This is the strictest option, instructing receiving mail servers that only the IP addresses explicitly specified in the [SPF record](/content/spf-records) are permitted to send emails on **behalf of the domain**. _Any emails originating from unauthorized sources should be rejected_. This policy offers the strongest protection against [email spoofing](https://www.bleepingcomputer.com/news/google/google-now-blocks-spoofed-emails-for-better-phishing-protection/), as it prevents unauthorized emails from being delivered.

[![email spoofing](https://media.mailhop.org/duocircle/images/2025/01/sender-policy-framework-5378.jpg)](https://media.mailhop.org/duocircle/images/2025/01/sender-policy-framework-5378.jpg)

## Fallback to DKIM

[DKIM](/resources/what-is-dkim) is one of the three primary email authentication protocols. This protocol is implemented at the sender’s end to help the **receiving server verify** if the email content was tampered with in transit. DKIM works on the basis of cryptographically secured public and [private keys](https://www.investopedia.com/terms/p/private-key.asp) that are matched by the recipient’s end. _If the keys don’t match, then it means someone has altered the email on its way_.

It’s complicated to keep up with email authentication protocols, especially when your risk tolerance is low and you use [dynamic IP addresses](https://www.geeksforgeeks.org/what-is-a-dynamic-ip-address/). Any mistake or missed move can wreck your [security posture](https://www.techtarget.com/searchsecurity/definition/security-posture), leaving you vulnerable to financial, reputational, social, and operational issues. But we at [DuoCircle](/) can **strengthen your defenses** against email-based menaces. Please contact us to learn how we can be mutually helpful.

![Brad Slavin](https://media.mailhop.org/dmarcreport/images/team/brad-slavin.jpg) 

Brad Slavin 

General Manager

General Manager at DuoCircle. Product strategy and commercial lead across the email security portfolio.

## Secure your email infrastructure

Protect, authenticate, and deliver. Contact our team to find the right solution.

[Contact Sales](/contact/) [Explore Products](/products/) 

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