Why do emails with SPF hard fail sometimes land in inbox instead of spam folder in Gmail?

Email marketer from Mailgun Support shares that although an SPF hard fail tells the receiving server the email should be rejected, the server may still choose to accept the email and deliver it to the inbox or spam folder. This is because the recipient server will take into account other factors and apply its own policies.

Email marketer from Email on Acid shares that recipient engagement is a major factor for getting emails into the inbox and that consistently good engagement can lead inbox providers to be more lenient regarding technical checks.

Marketer from Email Geeks shares that large domains have p=none for years as they test and cleanup odd-outs and that it would be very bad for to end up in the spam folder during testing

Email marketer from Reddit user u/email_expert responds that Gmail uses complex algorithms to determine inbox placement. SPF is just one piece of the puzzle. Positive engagement (opens, clicks) can override a technical failure like SPF.

Marketer from Email Geeks shares that a DMARC ‘fail’ verdict means that the message’s From domain cannot be reliably verified; it does not necessarily mean that the message was illegitimate or unauthorized and suspects that lots of data besides DMARC authentication results goes into the placement decision.

Email marketer from Quora says that Gmail prioritizes user experience. If users have marked similar emails as 'not spam' in the past, Gmail may be more likely to deliver the email to the inbox, even with an SPF failure.

Email marketer from ZeroBounce shares that even though it's not advisable, SPF records can be bypassed by spammers and phishers and it's possible they have found techniques that exploit vulnerabilities or weak configurations.

Email marketer from StackOverflow user User42 explains that mail servers can choose to ignore SPF records based on sender reputation. If a sender has a good reputation, the email may still make it to the inbox despite an SPF failure.

Email marketer from Email Marketing Forums states that it's likely Gmail is using machine learning to decide whether emails are genuine, rather than just relying on SPF. Content and sending habits are used in their determination.

Email marketer from SendGrid mentions a combination of factors including IP address reputation, domain reputation, authentication protocols, and content quality determine email deliverability. If other signals are strong, Gmail may still place the email in the inbox.

Email marketer from ActiveCampaign explains that email filters are complex and consider sender reputation, content, and user engagement. It shares that a strong reputation and positive user interactions can sometimes override technical authentication failures.

Email marketer from Constant Contact explains that Gmail trusts emails more if they're coming from a known sender and they have a higher sender reputation. They are more likely to be put into the inbox, even when the emails are not fully authenticated.

Expert from Spam Resource explains that in some cases, especially with forwarded mail, SPF checks can fail, and receivers must rely on other signals (like reputation) to determine deliverability.

Expert from Spam Resource explains that mailbox providers may choose to ignore SPF failures and rely on other signals, especially when there's a history of positive engagement from the recipient.

Expert from Email Geeks explains that spammers and phishers spend a lot of time testing how to get to the inbox and what will get past the filters and that this time they got it right, but It will take a couple days for the filters to catch up and then they’ll test again.

Documentation from DMARC.org shares that while SPF is an important authentication method, DMARC policy dictates how receiving mail servers should handle messages that fail SPF checks. A policy of 'none' allows messages to be delivered regardless of SPF results, and even a 'reject' policy may not be strictly enforced by all mail servers.

Documentation from RFC Editor explains that SPF provides a mechanism for verifying the sender's authorization to use a domain but that the receiving server has the ultimate authority on how to handle messages that fail SPF checks. It recommends policies, but doesn't mandate actions.

Documentation from Microsoft Learn shares that Microsoft uses a Spam Confidence Level (SCL) score that considers multiple factors, of which SPF is one. The SCL score determines whether a message goes to the inbox, junk folder, or is rejected. Factors like safe senders lists and rules can override SPF failures.

Documentation from Google Workspace Admin Help explains that Gmail considers SPF records during email authentication, but it's only one of many factors. A hard fail doesn't guarantee spam placement because Gmail also analyzes sender reputation, content, user behavior, and other signals to determine where to deliver a message.