Why did Yahoo and AOL emails experience false bounce errors in late 2019?

In late 2019, from approximately September through November, Yahoo and AOL email services, both operating under Verizon Media, experienced significant and widespread outages that resulted in legitimate emails being falsely rejected. These rejections typically manifested as hard bounce errors, specifically '554 5.7.1,' which normally signify permanent delivery failures. However, the issues were temporary and caused by severe internal server problems, system misconfigurations, or general instability and overload within Verizon Media's mail infrastructure. This meant valid emails were erroneously bounced regardless of sender reputation, compelling email marketers and server administrators to adapt by treating these hard bounces as temporary soft bounces and implementing retry mechanisms. The problems were largely resolved by late November, underscoring a critical recipient-side system error rather than any fault on the part of email senders.

The latter half of 2019 saw notable disruptions in email deliverability to Yahoo and AOL accounts, primarily due to unannounced service issues and widespread internal server failures at Verizon Media, their parent company. This led to a pervasive problem where legitimate emails were incorrectly rejected, often generating what appeared to be permanent hard bounce codes, such as the 554 DSN message. Despite these seemingly definitive rejections, the underlying cause was a temporary, systemic malfunction on the recipient's end, not an issue with the sending email's validity or sender reputation. Consequently, email marketers were advised to handle these erroneous hard bounces as temporary soft bounces, emphasizing the need for flexible handling and diligent monitoring during such critical infrastructure events.

During the latter part of 2019, specifically from September through November, Yahoo and AOL, including Verizon properties, encountered significant service interruptions that led to legitimate emails being incorrectly bounced. These incidents often presented as 554 5.7.1 errors, typically indicating a permanent failure due to spam or policy violations. However, the rejections were false, stemming from internal system malfunctions, misconfigurations, or software bugs within the email providers' infrastructure. This widespread problem affected senders universally, regardless of their established reputation or email content, signifying a major recipient-side issue rather than a sender-driven deliverability problem. Most of these technical glitches were rectified by late November, highlighting the complexity of email delivery systems and the importance of monitoring ISP health.

In late 2019, email services for Yahoo and AOL, both under Verizon Media, experienced significant technical glitches causing legitimate emails to be falsely rejected. These widespread temporary server issues mistakenly generated hard bounce errors, specifically 554 and 554 5.7.1 codes, which typically signify permanent delivery failures. However, the underlying cause was internal instability, overload, or severe system problems within Verizon Media's infrastructure, requiring senders to treat these as temporary failures and retry delivery. This anomaly highlighted a critical recipient-side system malfunction that led to valid messages being erroneously bounced.