Where will temporary errors manifest from Yahoo and Google's new email authentication policies?
Michael Ko
Co-founder & CEO, Suped
Published 8 Jun 2025
Updated 17 Aug 2025
5 min read
Google and Yahoo’s new email authentication requirements represent a significant shift for senders. While these policies aim to bolster email security and reduce spam, they also introduce a new layer of complexity and potential challenges for maintaining consistent email deliverability.
Many email senders are understandably concerned about how these changes will impact their existing mail flow. A particular point of concern revolves around temporary errors, or deferrals, which don't immediately result in permanent rejections but can still disrupt email campaigns and critical communications.
Understanding precisely where these temporary errors will manifest is crucial for timely troubleshooting and ensuring your emails continue to reach inboxes. This insight helps pinpoint issues related to SPF, DKIM, and DMARC compliance, allowing for quick remediation before problems escalate.
Temporary errors, commonly referred to as “soft bounces” or “deferrals,” indicate that an email could not be delivered on the first attempt but the receiving server is willing to try again later. Unlike hard bounces, which signify a permanent failure, deferrals suggest a transient issue. These can arise from various factors, such as a recipient’s mailbox being full, temporary server issues, or, increasingly, policy-based rejections stemming from the new authentication requirements.
With the new policies from Google and Yahoo, temporary errors serve as a crucial mechanism for mail providers to signal compliance issues without immediately blocking mail. This initial phase provides senders with an opportunity to identify and rectify misconfigurations before emails are permanently rejected or routed to spam folders. It acts as a grace period, but still necessitates diligent monitoring and prompt action.
These policies place a strong emphasis on strict email authentication. If your SPF, DKIM, or DMARC records are misconfigured or fail validation, temporary errors are typically the first line of defense. The overarching goal is to prompt senders to correct their authentication setup, thereby contributing to a significant reduction in the overall volume of unauthenticated or potentially malicious email traversing the internet.
Where errors will appear
The primary locations to observe temporary errors will be your SMTP server logs and, for high-volume senders, your Postmaster Tools accounts. SMTP responses deliver granular details about why an email was deferred, while Postmaster Tools offer an aggregated view of your sending reputation and error rates.
For Google, anticipate seeing specific SMTP response codes that clearly indicate authentication failures. For instance, a common temporary error related to authentication might initially manifest as a 4xx series code, which could then escalate to a 5xx series code (a permanent failure) if the underlying issues persist. This escalation is part of how Google will enforce new email authentication requirements.
Yahoo (including AOL Mail) will also utilize SMTP responses to communicate deferrals associated with their updated policies. While specific new codes for authentication failures are still being introduced or clarified, you can generally anticipate codes such as 421, 451, or 452, all of which indicate a temporary issue. It is essential to continuously monitor Yahoo's SMTP error codes page for the most current information. Persistent issues can lead to your domain or IP being added to a blocklist (or blacklist).
Specific error codes and how to interpret them
One notable Google SMTP error code to particularly watch for is 5.7.26, which unequivocally signals an authentication failure. While this is categorized as a permanent failure code, during the initial phases of enforcement, you might encounter more temporary 4xx errors preceding this. The 5.7.26 error explicitly states that the message either lacks proper authentication (SPF or DKIM) or fails authentication checks, resulting in the message being blocked.
Deciphering these SMTP responses is absolutely critical for effective debugging. A 4xx response indicates a “temporary failure,” prompting your sending server to retry the delivery. However, if the underlying authentication issue remains unaddressed, these temporary failures will inevitably escalate to permanent rejections. This underscores the paramount importance of vigilant DMARC monitoring and ensuring timely SPF, DKIM, and DMARC updates.
Here’s a breakdown of how authentication failures might present themselves and an example of Google'sGmail SMTP errors and codes for a 5.7.26 error.
Google's 5.7.26: This error indicates messages without proper authentication or those failing SPF or DKIM checks. While it is a permanent block, initial policy enforcement may show temporary warnings before this.
Yahoo deferrals: Look for 4xx SMTP codes, such as 421 or 451, which indicate temporary issues that will become permanent failures if not addressed promptly.
General deferrals: Any email not meeting the new standards may experience increased deferrals, even if specific new codes aren't immediately visible, due to overall lowered sender reputation.
Google SMTP 5.7.26 error examplePlain text
550, "5.7.26", "This message does not have authentication information or fails to pass authentication checks (SPF or DKIM). To best protect our users from spam, the message has been blocked. Please visit Prevent mail to Gmail users from being blocked or sent to spam for more information."
Before authentication policies
Email messages might be accepted even with missing or misconfigured SPF, DKIM, or DMARC records, often landing in spam or junk folders without explicit deferrals.
Deliverability: Inconsistent, reliant on general sender reputation.
Troubleshooting: Difficult to pinpoint authentication issues, as explicit error messages were less common.
Risk: Higher risk of spoofing and phishing attempts due to lax authentication enforcement.
After authentication policies
Unauthenticated or improperly authenticated email will be met with immediate temporary deferrals, escalating to permanent rejections if issues persist.
Deliverability: Requires strict SPF, DKIM, and DMARC compliance for inbox placement.
Troubleshooting: Specific SMTP error codes and Postmaster Tools data provide clear indicators for failed authentication.
Risk: Reduced spam and phishing, but increased risk of legitimate email being deferred or blocked for non-compliance.
Views from the trenches
Best practices
Implement DMARC with a p=none policy initially to monitor reports without impacting delivery.
Ensure all sending IP addresses and domains are properly authorized in your SPF record.
Verify DKIM signatures for all outbound email streams from your domain.
Regularly check Google Postmaster Tools for any new delivery errors or reputation drops.
Common pitfalls
Ignoring DMARC aggregate reports, which means missing crucial authentication failures.
Overlooking SPF void lookups or hardfail policies that incorrectly block legitimate mail.
Not updating DKIM selectors when changing email service providers, causing issues.
Assuming emails are delivered if they don't hard bounce immediately, which is a mistake.
Expert tips
Use DMARC forensic reports to identify specific sources of authentication failures for precise remediation.
Configure alerts for significant changes in bounce rates or spam classifications in Postmaster Tools.
Regularly validate your SPF, DKIM, and DMARC records using online tools to catch misconfigurations early.
Segment your email sending by stream to identify which types of emails or platforms are causing issues.
Marketer view
Marketer from Email Geeks says temporary errors will manifest in Google Postmaster Tools as delivery error data, detailing the specific reasons.
February 1, 2024 - Email Geeks
Marketer view
Marketer from Email Geeks says senders will receive dedicated SMTP responses that indicate temporary email authentication issues.
February 2, 2024 - Email Geeks
Adapting to the new email landscape
The changes introduced by Google and Yahoo signify a pivotal moment in the evolution of email security and deliverability. Temporary errors are not merely minor inconveniences, but rather critical signals indicating an immediate need for action regarding your email authentication setup.
Proactive monitoring of your SMTP logs and Postmaster Tools, coupled with a comprehensive understanding of specific error codes, will be key to successfully navigating these new requirements. Swiftly resolving these temporary deferrals is paramount to prevent them from escalating into permanent delivery failures and potential blocklisting (or blacklisting) of your domain.
By embracing robust email authentication protocols like SPF, DKIM, and DMARC and remaining vigilant, senders can ensure their legitimate emails consistently reach the inbox, thereby maintaining a strong sender reputation and effective communication channels.
Google and 
Yahoo, temporary errors serve as a crucial mechanism for mail providers to signal compliance issues without immediately blocking mail. This initial phase provides senders with an opportunity to identify and rectify misconfigurations before emails are permanently rejected or routed to spam folders. It acts as a grace period, but still necessitates diligent monitoring and prompt action.
AOL Mail) will also utilize SMTP responses to communicate deferrals associated with their updated policies. While specific new codes for authentication failures are still being introduced or clarified, you can generally anticipate codes such as 421, 451, or 452, all of which indicate a temporary issue. It is essential to continuously monitor Yahoo's SMTP error codes page for the most current information. Persistent issues can lead to your domain or IP being added to a blocklist (or blacklist).
