SPF Neutral Mechanism Explained

The SPF neutral mechanism “?all” is a mechanism in the Sender Policy Framework (SPF) records that results in a neutral evaluation. It instructs receiving servers not to make a pass or fail decision based on SPF.

• Example SPF record with ?all:
  v=spf1 include:_spf.google.com ?all

In this example, the domain includes Google’s SPF settings but ends with `?all`, which tells receiving servers to take a neutral stance on other senders. It doesn’t approve or reject them, offering no clear judgment.

While technically valid, `?all` can create ambiguity that weakens trust, and may lead to delivery issues if misused.

SPF Neutral Mechanism (?all) vs. Other Mechanisms

“The domain owner has explicitly stated that he cannot or does not want to assert whether or not the IP address is authorized.  A “Neutral” result MUST be treated exactly like the “None” result; the distinction exists only for informational purposes.  Treating “Neutral” more harshly than “None” would discourage domain owners from testing the use of SPF records.” – RFC 4408

The “?all” mechanism differs from other SPF qualifiers because it provides no pass/fail result, which can hinder DMARC evaluation and mail server decision-making. 

The “?all” mechanism can confuse receiving mail servers, and they won’t know if they should trust the email or not. The table below provides a concise summary of the effects and use cases of the different mechanisms. 

When to Use the SPF Neutral Mechanism

The SPF neutral mechanism is not recommended for most modern email setups. It may still be used in some cases while exercising caution and planning for a transition to more secure mechanisms in advance. 

Legacy Systems

Some older infrastructure and systems may not have clear sender policies or proper SPF handling in place. In such cases, you will need a neutral stance, like with the SPF neutral mechanism, to maintain functionality.

Testing Phase

You can also use this mechanism during the initial SPF implementation. It will allow domain owners to monitor email traffic while keeping delivery intact, making it safe to use it as a starting point.

Rare Edge Cases

Sometimes, other mechanisms like ~all or -all may cause unexpected deliverability problems. To diagnose these issues, you can temporarily use the ?all mechanism. 

⚠️ SPF mechanisms are evaluated sequentially, and placing ?all before other mechanisms can cause SPF evaluation to stop early, potentially bypassing intended checks.

What Are the Risks of Using ?all

The ?all mechanism prevents clear authentication outcomes, which undermines both email security (e.g., spoofing protection) and email deliverability. Possible risks include: 

Email Spoofing

Since ?all returns a neutral result, it provides no defense against spoofing. In contrast, ~all and -all return identifiable fail signals. When combined with an enforced DMARC policy, these signals allow receiving servers to quarantine or reject unauthorized emails.

DMARC Conflicts

Neutral SPF results from ?all may still technically align with DMARC if the domains match, but they provide no pass/fail signal, which DMARC requires to take enforcement action.

Deliverability Issues

Some mail servers interpret the ?all mechanism (neutral) in SPF as a weak or non-committal policy. This can signal poor enforcement of sender identity, potentially reducing trust. Mail providers like Gmail use multiple signals, and a weak SPF policy can be just one of many factors.