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

Summary

In late 2019, many email senders experienced a peculiar issue with Yahoo and AOL email addresses: receiving false bounce errors indicating that user accounts did not exist. This problem led to significant false positive bounce rates, sometimes as high as 25% for affected senders. Despite these bounce messages, the same email addresses often received mail successfully days or weeks later, highlighting the erroneous nature of the initial bounces. This temporary anomaly was a point of concern for marketers relying on accurate deliverability metrics.

What email marketers say

Email marketers widely reported a noticeable uptick in false bounce errors from Yahoo and AOL domains in late 2019. This anomaly caused frustration, as it incorrectly flagged valid recipients as non-existent. Marketers had to discern whether these bounces reflected actual invalid addresses or were a temporary system malfunction, impacting their campaigns and list hygiene efforts. This experience underscored the importance of robust monitoring and understanding ISP-specific behaviors.

Marketer view

Email Marketer from Email Geeks observed false bounce reasons from Yahoo within a month. Their analysis showed Yahoo throwing a "554 delivery error: dd This user doesn't have a yahoo.com account" message, despite the email being valid.

30 Sep 2019 - Email Geeks

Marketer view

Marketer from Spiceworks Community reports a significant increase in bounce-back messages from Yahoo email addresses over the past week, indicating an ongoing issue.

22 Mar 2024 - Spiceworks Community

What the experts say

Experts in email deliverability quickly identified the false bounce errors from Yahoo and AOL in late 2019 as a known, albeit temporary, issue. While some initially attributed it solely to Verizon domains and specific header requirements, further investigation confirmed that Yahoo and AOL were indeed affected. The consensus was that these were erroneous rejections on the mailbox provider's side, rather than a problem with the sender's email list or sending practices.

Expert view

Expert from Email Geeks (U3HV54286) confirmed there was a problem with Yahoo falsely rejecting emails around the end of September 2019, aligning with the reported timeline of the issue.

13 Nov 2019 - Email Geeks

Expert view

Expert from Word to the Wise reported an uptick in user unknown responses for Verizon email addresses during October 2019, specifically noting the "554 delivery error" message indicating an invalid recipient.

04 Oct 2019 - Word to the Wise

What the documentation says

While specific official documentation from Yahoo or AOL regarding this precise incident in late 2019 may be scarce, the observed bounce codes and their subsequent resolution align with known behaviors of large mailbox providers. Such issues often stem from temporary server-side glitches, maintenance, or misconfigurations that lead to incorrect rejection reasons. The recovery from these false bounces typically occurs without direct intervention from senders, as the underlying problem lies with the recipient's email infrastructure.

Technical article

Documentation from Word to the Wise explains that a 550 error typically indicates a permanent rejection, such as a nonexistent mailbox. However, unusual circumstances can lead to false 550 responses.

04 Oct 2019 - Word to the Wise

Technical article

Documentation from Quora suggests that when an email is sent to an unused domain, the DNS lookup will fail, prompting the local mail agent to send an error message to the sender, often a 550 bounce.

20 Nov 2019 - Quora

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