What are the considerations for using soft fail vs hard fail in SPF policies?
Matthew Whittaker
Co-founder & CTO, Suped
Published 27 May 2025
Updated 19 Aug 2025
9 min read
When setting up Sender Policy Framework (SPF) records for your domain, one of the most critical decisions you face is whether to use a soft fail (~all) or a hard fail (-all) policy. This choice dictates how recipient mail servers should treat emails that fail SPF authentication, and it significantly impacts your email deliverability and security posture.
Understanding the nuances of these two mechanisms is vital, especially since SPF, when used alone, has limitations. Many organizations pair SPF with DKIM and DMARC to create a robust email authentication ecosystem. Your choice of SPF policy needs to align with your overall email security strategy and the maturity of your deployment.
We'll explore the implications of each approach, helping you decide what's best for your domain. The primary goal is always to ensure legitimate emails reach their intended recipients while minimizing the risk of spoofing and phishing.
SPF (Sender Policy Framework) records are DNS TXT records that specify which mail servers are authorized to send email on behalf of your domain. The mechanism at the end of an SPF record, such as ~all (soft fail) or -all (hard fail), tells recipient mail servers what to do if an email originates from an unauthorized IP address.
Soft fail (~all)
A soft fail policy indicates that emails from unauthorized senders should be accepted but marked as suspicious. The ~all qualifier suggests that while the sending server is probably not authorized, the email should not be outright rejected. Instead, it might be delivered to the recipient's spam or junk folder, or further analyzed by other authentication mechanisms like DMARC.
Hard fail (-all)
In contrast, a hard fail policy is a definitive statement that any email not originating from a server explicitly listed in your SPF record is unauthorized and should be rejected. The -all qualifier tells recipient mail servers to discard messages that fail SPF checks. This is the most aggressive policy and aims to prevent unauthorized emails from reaching inboxes entirely.
Example SPF soft fail recordDNS
v=spf1 include:_spf.example.com ~all
The choice between these two largely depends on your confidence in your SPF record's completeness and your tolerance for potential legitimate email rejections.
The role of DMARC in SPF policy
DMARC (Domain-based Message Authentication, Reporting, and Conformance) plays a pivotal role in modern email authentication. It instructs recipient servers on how to handle emails that fail SPF or DKIM checks, and it provides valuable feedback to domain owners through aggregate reports. When DMARC is properly implemented, its policy can significantly influence how SPF failures are treated.
If a domain has a DMARC policy in place (e.g., p=quarantine or p=reject), an SPF soft fail (~all) is generally preferred. This is because DMARC's policy (quarantine or reject) will handle the ultimate disposition of the email if both SPF and DKIM fail to align. A hard fail (-all) with DMARC in place offers no additional security benefits over ~all and can lead to unintended blocking of legitimate emails before DMARC has a chance to evaluate the message's authenticity through DKIM. We often see mail servers reject emails based on SPF hard fail before processing DKIM or DMARC.
In a robust setup with DMARC, SPF and DKIM act as positive assertions, confirming the legitimacy of mail. DMARC then serves as the central authority for negative policy assertions, handling what happens when authentication fails. This separation of concerns simplifies troubleshooting and provides greater control over email flow. For domains actively using DMARC, particularly with a p=quarantine or p=reject policy, a soft fail is almost always the recommended approach.
A soft fail policy is typically recommended during the initial deployment of SPF and DMARC, or for domains with complex and frequently changing email sending infrastructures. It provides a safer approach, allowing you to monitor and adjust your records without immediately blocking legitimate emails.
When to choose soft fail
Initial deployment: Start with ~all to avoid disrupting email flow while you identify all legitimate sending sources.
Complex infrastructure: If you have many third-party senders or frequently update your email services, ~all minimizes the risk of inadvertently blocking valid emails. This is especially true if you are prone to SPF DNS lookup limits.
Forwarded emails: Emails that are forwarded often break SPF authentication. ~all allows these to be delivered, while DMARC handles any further policy decisions.
DMARC deployment: If you have DMARC in place, especially with p=none, p=quarantine, or p=reject, ~all is the recommended choice. This allows DMARC to make the final decision based on both SPF and DKIM alignment, as explained by Al in his article.
Implementing ~all allows you to collect DMARC reports and identify all legitimate sending sources before moving to a stricter enforcement. This gradual approach minimizes the risk of blocking emails that should be delivered, helping you resolve SPF SOFTFAIL errors and fine-tune your configuration.
Considerations for hard fail
While a hard fail policy provides the strongest signal to recipient mail servers that unauthorized emails should be rejected, it comes with significant risks, especially if your SPF record is not perfectly maintained or if you're not using DMARC effectively.
Risks of hard fail
Blocking legitimate emails: If you miss even one authorized sending source in your SPF record, emails from that source will be rejected, potentially leading to lost communications and deliverability issues.
Interference with DMARC: Some smaller Mailbox Providers (MBPs) might reject emails based on a hard SPF fail before conducting DKIM or DMARC checks. This can lead to unexpected blocking even if your DMARC policy would otherwise allow the email to pass due to DKIM alignment. This is why it's crucial to consider whether hard fail should be enforced with DMARC.
Increased troubleshooting: Hard fails can be challenging to troubleshoot, as rejected emails provide little to no feedback, making it harder to identify the root cause of deliverability problems.
Due to these risks, a hard fail is typically only considered for domains that have a very stable and well-documented sending infrastructure, are confident that their SPF record is exhaustive, and have a robust DMARC implementation that can provide sufficient visibility and control.
Comparing soft fail and hard fail
Soft fail (~all)
Email disposition: Messages are accepted but marked as suspicious, potentially sent to spam.
Error tolerance: More forgiving of configuration errors, reducing the chance of blocking legitimate emails.
DMARC integration: Works seamlessly with DMARC, allowing it to make the ultimate policy decision based on both SPF and DKIM.
Deployment phase: Ideal for initial SPF and DMARC rollout and ongoing monitoring.
Hard fail (-all)
Email disposition: Messages are immediately rejected at the recipient server.
Error tolerance: Zero tolerance for errors, increasing the risk of blocking legitimate emails due to misconfiguration.
DMARC integration: Can sometimes bypass DMARC, leading to premature rejection before full authentication evaluation.
Deployment phase: Generally not recommended if DMARC is also in use, or for domains with dynamic sending environments.
Choosing the right SPF policy is about balancing security with deliverability. For most organizations, especially those leveraging DMARC, a soft fail policy is the safer and more effective choice. It allows you to enforce strong authentication through DMARC without risking the accidental blocking of valid emails.
If you're setting up SPF for the first time or suspect there might be unknown sending sources, definitely start with ~all. This provides time to gather data from DMARC reports and perfect your SPF record before moving to a stricter enforcement. Remember, SPF is just one layer of email authentication, and its effectiveness is significantly enhanced when combined with DKIM and DMARC.
Views from the trenches
In the world of email, balancing robust security with reliable deliverability is a constant challenge. Our community has shared various insights on SPF policies.
Best practices
Always begin your SPF implementation with a soft fail policy, especially if DMARC is not yet fully configured.
Regularly review your DMARC reports to identify all legitimate sending sources before considering a stricter SPF policy.
Ensure your SPF record is updated every time you add or remove an email sending service to prevent deliverability issues.
Prioritize DMARC's reject policy over SPF hard fail when you have DMARC in place, as DMARC provides better control.
Common pitfalls
Immediately deploying SPF with a hard fail, which can lead to legitimate emails being blocked.
Neglecting to monitor DMARC reports, thus missing important insights into SPF failures and legitimate email sources.
Forgetting to update SPF records when migrating email systems or adding new third-party senders.
Assuming SPF alone offers full protection against spoofing without the aid of DKIM and DMARC.
Expert tips
Use SPF record flatteners if your record approaches the 10 DNS lookup limit to avoid validation failures.
Familiarize yourself with RFC 7208 sections on soft fail implications for comprehensive understanding.
Employ a DMARC monitoring solution to gain granular visibility into how recipient servers handle your SPF and DKIM authenticated emails.
Test your SPF record thoroughly before pushing any changes to production, using an email deliverability tester.
Expert view
Expert from Email Geeks says a hard fail (-all) can sometimes cause blocking before checking for DKIM, particularly at smaller Mailbox Providers. A soft fail (~all) is generally better as it passes the blocking decision to the DMARC policy.
2024-04-30 - Email Geeks
Expert view
Expert from Email Geeks says the M3AAWG’s Email Authentication Best Practices specifically recommends using a soft fail. A hard fail risks premature rejection before messages can be fully parsed for DKIM and DMARC checks.
2024-04-30 - Email Geeks
The path forward for SPF policies
The decision between SPF soft fail and hard fail is not a one-size-fits-all answer. For most organizations, especially those in the process of, or already having implemented, DMARC, a soft fail (~all) is the safer and more recommended approach. It minimizes the risk of inadvertently blocking legitimate emails and allows DMARC to take the lead in defining policy for unauthenticated messages.
A hard fail (-all) should be reserved for mature domains with static sending infrastructures and a clear understanding of all their sending sources, and only after DMARC has been fully deployed to an enforcement policy. Always aim for a gradual rollout, using DMARC reports to refine your SPF record and achieve optimal email deliverability and security.
