Why are AOL and Yahoo emails bouncing and how can it be fixed?
Matthew Whittaker
Co-founder & CTO, Suped
Published 3 Aug 2025
Updated 14 Aug 2025
8 min read
Summary
Many senders frequently encounter unexpected email bounces from AOL and Yahoo, a recurring challenge in email deliverability. These issues, ranging from soft bounces with specific error codes like TSS04 to hard bounces indicating non-existent addresses, often stem from dynamic factors. Key among these are the shared infrastructure between AOL and Yahoo, leading to combined volume thresholds, and the stringent anti-spam measures these mailbox providers employ.
Key findings
Bounce types: Bounces can be soft, often including the TSS04 code, or hard, like email does not exist, particularly for Yahoo and Gmail addresses.
Infrastructure shift: AOL's email addresses now leveraging Yahoo's infrastructure can cause senders to hit new, stricter volume thresholds they previously avoided.
Unforeseen spikes: Bounce rate spikes can occur suddenly, even if sending practices have remained consistent. This often indicates a change in how the receiving ISP views your mail, perhaps due to increased complaints or a perceived shift to spam.
New sign-up issues: A significant portion of bounces affecting new sign-ups with email does not exist errors may point to issues with real-time validation or list acquisition processes.
Key considerations
Email authentication: Ensure your domain has correctly configured SPF, DKIM, and DMARC records. These records are crucial for validating your sending domain and preventing email authentication failures, a common reason for bounces.
List hygiene: Regularly clean your email list by removing unengaged or inactive contacts. This practice minimizes bounces and improves overall sender reputation. Consider also why soft bounces might be occurring for a proactive approach.
Throttling sends: For specific domains like AOL and Yahoo, consider throttling your email volume over longer periods (hours or days) to avoid hitting arbitrary rate limits. The eM Client forum highlights that most global mail servers now require specific records in all sending domains.
Monitoring and analysis: Pay close attention to bounce codes and patterns. Identifying the specific type of bounce (e.g., TSS04) can provide clues to the underlying problem, whether it's related to content, volume, or reputation. Add required records to your domain.
What email marketers say
Email marketers frequently share experiences of sudden and unexplained increases in bounce rates, particularly from AOL and Yahoo addresses. Their insights often point to the unpredictable nature of ISP filtering, especially since the integration of AOL into Yahoo's infrastructure. Many report hitting new thresholds or facing scrutiny even without changes in their sending habits, underscoring the dynamic challenges of maintaining good deliverability with these providers.
Key opinions
Spike in bounces: Many marketers report experiencing sudden spikes in AOL bounces, sometimes appearing out of nowhere.
TSS04 soft bounces: The TSS04 bounce text from Yahoo indicates potential issues with complaints or a spam pattern.
Infrastructure merger impact: The shift of AOL addresses to Yahoo's infrastructure is believed to cause senders to cross previously unreached thresholds, leading to more bounces.
New subscriber issues: A high percentage of bounces are observed for newly signed-up users, with errors like email does not exist, even for seemingly valid addresses. For more on this, see why valid addresses bounce.
Key considerations
List hygiene importance: Regularly cleaning email lists, especially removing less engaged contacts, can significantly reduce bounce rates.
Engagement strategy: Prioritizing sending to highly engaged users and adjusting automated flows based on initial engagement (e.g., opens) can help mitigate bounces. This also helps when AOL and Yahoo flag emails as spam.
Send throttling: Throttling delivery over longer periods, sometimes hours or days, can alleviate pressure on Yahoo and AOL servers. HubSpot community indicates this type of error tends to occur when throttling happens.
Complaint impact: A sudden increase in complaints can trigger soft bounce activity and signal to ISPs that your sending patterns resemble spam.
Marketer view
Email marketer from Email Geeks observed a sudden rise in AOL bounces during a specific week, particularly on a recent day, despite no changes in sending practices.
14 Mar 2019 - Email Geeks
Marketer view
Marketer from Spiceworks Community noted a really sharp increase in errors and bounce-back messages from Yahoo email addresses for several users.
17 Jan 2024 - Spiceworks Community
What the experts say
Deliverability experts provide crucial insights into the complexities of AOL and Yahoo bounces, often linking them to the unified infrastructure (now Oath) and sophisticated spam detection algorithms. They emphasize that while some issues may seem to appear out of nowhere, they are typically a response to perceived shifts in sender reputation, user engagement, or a failure to adapt to evolving ISP requirements.
Key opinions
Complaint correlation: The TSS04 error for Yahoo soft bounces often correlates with increased user complaints or indicates a pattern that is being flagged as spam.
Threshold impacts: Experts suggest that the integration of AOL addresses into Yahoo's (Verizon Media's) infrastructure means senders might exceed volume thresholds they previously did not, leading to increased bounce rates. Understanding high bounce rates from Verizon is key.
List hygiene efficacy: Consistent list hygiene, including the removal of inactive or less engaged contacts, is a fundamental strategy to prevent bounces and improve deliverability. This also reduces the chances of your emails being blocked by Yahoo/AOL.
Volume management: Paring down sending volume and prioritizing engaged users, alongside throttling delivery, are proven methods to improve inbox placement and reduce bounces.
Key considerations
Reputation monitoring: Even without changes in sending behavior, sudden increases in bounces may indicate a shift in your domain or IP reputation, necessitating diligent reputation monitoring.
Bounce differentiation: Understanding the distinction between hard and soft bounces is critical for proper diagnosis and corrective action. For example, broken bounce handling can lead to further issues.
Engagement segmentation: Segmenting your audience by engagement levels and sending fewer emails to less active users can significantly improve deliverability to sensitive providers like AOL and Yahoo.
Blocklist implications: Increased bounces can lead to your domain or IP being placed on an email blocklist (or blacklist), which will further impair your deliverability. Learn what being blacklisted means.
Expert view
Expert from Email Geeks suggested that if an email from Yahoo includes the TSS04 bounce text, it often signifies an increase in complaints or indicates a pattern that Yahoo's systems believe is spam.
14 Mar 2019 - Email Geeks
Expert view
Expert from Spam Resource highlighted that some organizations suffer delivery issues due to security breaches, which can make their domains more susceptible to being flagged by ISPs like Yahoo and AOL. This can lead to increased bounces and broader email deliverability challenges.
20 May 2019 - Spam Resource
What the documentation says
Official documentation from major mailbox providers like AOL and Yahoo often provides crucial guidelines for senders to ensure optimal deliverability. These resources typically emphasize adherence to email authentication standards, content best practices, and active monitoring of sender reputation. They also shed light on common reasons for bounces, such as temporary rate limits, spam filtering, and non-existent user accounts.
Key findings
Authentication requirements: Mail servers, including those used by Yahoo and AOL, increasingly require proper authentication records (SPF, DKIM, DMARC) for all sending domains to accept incoming mail. Learn how to fix DMARC failing for Yahoo/AOL.
Spam blocking: Repeated delivery failure errors to AOL Mail customers are frequently attributed to spam blocking on AOL's servers, emphasizing the need for good sending practices.
Throttling and soft bounces: Soft bounces can occur when ISPs like Yahoo/AOL decide to throttle emails due to various factors, including volume or perceived suspicious patterns. For more information, read about soft bounce errors.
Account management: Yahoo has historically purged abandoned or inactive accounts, which can lead to legitimate-looking addresses suddenly bouncing as non-existent.
Key considerations
Compliance with policies: Adhering to the specific policies and guidelines published by AOL, Yahoo, and their parent company (Oath/Verizon Media) is crucial for consistent deliverability. This includes understanding the troubleshooting DMARC reports from these providers.
Filter and block settings: For recipients, AOL's help documentation advises checking personal email filters and block settings as a first step if emails are not being received. Fix problems receiving AOL Mail.
Content and attachments: Problems with viewing images or attachments in emails can sometimes be related to how the email is formatted or perceived by the receiving server, potentially contributing to non-delivery or spam flagging.
Security breaches impact: Past security breaches at Yahoo and AOL have influenced their stronger spam defenses and DMARC enforcement, which can impact mailing lists and forwarding.
Technical article
AOL Help states that if you are repeatedly getting delivery failure errors when sending messages to AOL Mail customers, it is most likely due to spam blocking on AOL's servers. They advise senders to review their practices.
20 Feb 2024 - help.aol.com
Technical article
TidBITS reports that Yahoo and AOL made sweeping changes, possibly after significant security breaches, which allowed bad actors to exploit their systems, thus damaging mailing lists and email forwarding capabilities.
