Summary
Temporary errors resulting from Yahoo and Google's new email authentication policies manifest in various ways across different systems and reports. These errors may surface as delivery error data within Google Postmaster Tools (GPT), specific SMTP error codes like 5.7.26, soft bounces in email marketing platforms, Delivery Status Notifications (DSNs) containing 4xx SMTP codes, delayed delivery due to queued messages, greylisting responses, email deferrals (often with 4xx codes), and temporary blocks due to suspected spam activity. The underlying causes are typically transient issues like temporary DNS problems, rate limiting, or greylisting, necessitating retries by the sending server.
Key findings
- GPT Delivery Errors: Delivery error data is visible within Google Postmaster Tools (GPT), providing insight into temporary issues.
- SMTP Error Codes: Specific SMTP error codes, particularly in the 4xx and 5.7.26 ranges, indicate authentication-related temporary failures.
- Soft Bounces: Email marketing platforms categorize temporary failures as soft bounces, triggering automated retry attempts.
- DSN Notifications: Delivery Status Notifications (DSNs) expose temporary errors through 4xx SMTP codes.
- Delivery Delays: Emails may experience delays as they are queued for retry by sending servers.
- Greylisting: Receiving servers might implement greylisting, temporarily rejecting emails to combat spam.
- Email Deferrals: Temporary failures often manifest as email deferrals with associated SMTP 4xx codes.
- Throttling/Blocking: Sending servers could be temporarily blocked or throttled due to perceived spam-like activity.
- Mail Logs: Greylisting responses and deferrals are shown in mail logs.
Key considerations
- Monitor GPT: Regularly monitor Google Postmaster Tools (GPT) for delivery error data to identify and address potential issues.
- Analyze SMTP Codes: Thoroughly analyze SMTP error codes in DSNs and other reports to diagnose the root causes of temporary failures.
- Handle Soft Bounces: Properly configure email marketing platforms to handle soft bounces through appropriate retry mechanisms.
- Understand Retries: Ensure sending systems and platforms support automatic retries for deferred messages, aligning with SMTP standards and recommendations.
- Monitor Mail Logs: Implement monitoring of mail server logs to detect patterns of greylisting and deferrals.
- Maintain Reputation: Actively manage sender reputation to prevent throttling and blocking due to suspected spam-like activities.
- Monitor Deliverability Reports: Regularly check deliverability reports to spot the signs of issues.
What email marketers say
6 marketer opinions
Temporary errors resulting from Yahoo and Google's new email authentication policies can manifest in several ways. These include delivery error data in GPT, specific SMTP error codes (e.g., 5.7.26), soft bounces reported by email marketing platforms, Delivery Status Notifications (DSNs) containing 4xx SMTP codes, delayed email delivery as messages are queued for retry, and visibility in delivery reports.
Key opinions
- GPT Error Data: Temporary errors are reported in GPT (presumably Google Postmaster Tools or similar) as delivery error data with associated reasons.
- Specific SMTP Errors: Google's policy changes may result in a 5.7.26 SMTP error code indicating authentication failures.
- Soft Bounces: Email marketing platforms categorize temporary failures as soft bounces and typically retry delivery.
- DSN Notifications: Delivery Status Notifications (DSNs) will contain 4xx SMTP codes to indicate a temporary failure.
- Delivery Delays: Temporary errors can delay email delivery as messages are queued and retried.
- Delivery Reports: Error codes and issues stemming from temporary errors will surface in email delivery reports.
Key considerations
- Monitoring GPT: Regularly monitor GPT or similar tools for delivery error data to identify and address temporary issues.
- Handling Soft Bounces: Understand how your email marketing platform handles soft bounces and ensure appropriate retry settings are configured.
- DSN Analysis: Analyze DSNs to identify and troubleshoot the root causes of temporary delivery failures.
- Delivery Report Review: Actively review delivery reports for error codes and patterns that indicate authentication or temporary issues.
- Error Codes: Be familiar with SMTP 4xx codes to understand common problems.
Marketer view
Email marketer from Reddit explains that temporary errors will be visible in the Delivery Status Notifications (DSN) also known as bounce messages. They will contain 4xx SMTP codes
14 Nov 2021 - Reddit
Marketer view
Email marketer from Email Geeks explains that temporary errors will show up in GPT as Delivery Error data along with the reason for the temp error.
7 Apr 2025 - Email Geeks
What the experts say
2 expert opinions
Temporary errors from Yahoo and Google's new email authentication policies will manifest as greylisting responses and email deferrals. Greylisting temporarily rejects emails, requiring the sender to retry. Email deferrals are often accompanied by SMTP codes starting with 4 or blocks noting throttling from suspected spam and a suggested retry time.
Key opinions
- Greylisting: Receiving servers may use greylisting, which temporarily rejects emails and requires senders to retry later.
- Email Deferrals: Temporary failures often present as email deferrals with SMTP 4xx codes.
- Throttling Blocks: Messages may be temporarily blocked due to suspected spam activity, with a retry time indicated.
Key considerations
- Mail Log Monitoring: Monitor mail logs for greylisting responses to identify potential deliverability issues.
- SMTP Error Code Analysis: Analyze SMTP 4xx error codes to understand the reasons for temporary deferrals.
- Retry Schedules: Ensure sending systems are configured to retry sending deferred emails according to the suggested retry times.
- Sender Reputation: Address and mitigate spam-like sending behaviors to prevent being throttled or blocked.
Expert view
Expert from Word to the Wise explains that temporary errors may appear as greylisting responses, where the receiving server temporarily rejects the email to combat spam and requires the sending server to retry later, which will manifest in mail logs.
23 Oct 2021 - Word to the Wise
Expert view
Expert from Spamresource explains that temporary failures will often appear as deferrals of email either with an SMTP code starting in 4 or temporarily blocked with a message similar to “throttled due to detected spam activity”. These are usually accompanied by a retry time at which point the system believes it will be able to accept the message.
5 Nov 2022 - Spamresource
What the documentation says
3 technical articles
Temporary errors related to email authentication policies in Gmail and Yahoo Mail manifest as 4xx series SMTP error codes, particularly 421. These errors often stem from transient problems such as temporary DNS issues, rate limiting, or greylisting. The sending server should retry delivery. RFC 5321 defines 4xx codes as temporary failures that prompt the mailer to retry automatically.
Key findings
- 4xx SMTP Errors: Gmail and Yahoo Mail report temporary errors as 4xx series SMTP error codes.
- Specific 421 Code: Yahoo Mail may specifically use the 421 SMTP response code for temporary failures.
- Transient Problems: Typical causes for these errors are temporary DNS issues, rate limiting, or greylisting.
- Automatic Retries: SMTP protocol (RFC 5321) dictates that mailers will automatically retry sending emails that receive a 4xx error code.
Key considerations
- DNS Stability: Ensure your DNS infrastructure is stable to minimize temporary DNS resolution failures.
- Rate Limiting: Adhere to sending rate limits imposed by Gmail and Yahoo Mail to avoid triggering temporary errors.
- Greylisting Handling: Be prepared for greylisting by implementing a retry mechanism for temporarily rejected emails.
- SMTP Compliance: Ensure your email sending system complies with SMTP standards for retrying messages upon receiving temporary error codes.
Technical article
Documentation from Yahoo Help Central shares that temporary failures may lead to 421 SMTP response codes. These are usually associated with temporary server issues, rate limiting, or greylisting, requiring the sender to retry delivery.
15 Dec 2024 - Yahoo Help Central
Technical article
Documentation from RFC 5321 defines SMTP reply codes where 4xx is a temporary failure and 5xx is permanent. If the user does nothing then the mailer will retry. Specific error examples aren't provided in RFC it provides a framework.
9 Nov 2021 - RFC 5321
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