Summary
Since August 2024, many email senders have reported a significant and abnormal increase in 'mailbox full' bounce messages from Gmail addresses. This widespread issue has affected various sending platforms and IPs, pointing towards a systemic change rather than isolated incidents specific to individual senders. The bounces are frequently accompanied by the SMTP error code 554-5.4.7, which often includes a transient 452-4.2.2 message indicating insufficient storage space. This problem has led to frustration among email marketers and deliverability professionals who previously saw successful deliveries to these same addresses, sometimes just days before the bounces began. Understanding the core reasons for these bounces is crucial for maintaining healthy email sending practices.
Key findings
- Widespread issue: Multiple senders and ESPs reported experiencing the same spike in Gmail 'mailbox full' bounces since mid-August 2024, indicating a broader systemic change rather than isolated deliverability problems.
- Policy change: Google has implemented a stricter enforcement of mailbox quotas, beginning around August 15th. Previously, Gmail might have accepted messages even if an inbox was over quota, but this is no longer the case.
- Unified storage: Gmail's storage quota is tied to all Google services (Gmail, Google Drive, Google Photos). A user might have an empty inbox, but their overall Google account storage could be full due to other data, leading to bounces.
- Engagement vs. bounces: Many addresses that are now bouncing were recently engaged, having received and interacted with emails just days before the 'mailbox full' errors occurred. Some recipients even reported not receiving password resets despite their storage not appearing full.
- Deferral vs. hard bounce: The common SMTP error 554-5.4.7 often includes an internal 452-4.2.2 code, indicating a deferral (temporary issue) that ESPs may be incorrectly classifying as a hard bounce (permanent). This nuance is important for proper handling, as discussed by MailBluster regarding bounce types.
Key considerations
- Audience review: Investigate whether the bouncing addresses have a common history, such as being less engaged or recently added to lists, even if the overall audience has not changed significantly.
- Bounce categorization: Verify how your ESP classifies 'mailbox full' bounces. If deferrals are being treated as hard bounces, it could lead to premature suppression of otherwise valid addresses.
- Suppression strategy: Consider implementing a temporary suppression period for 'mailbox full' bounces, followed by retries. If the bounces persist, then consider permanent suppression to protect your sender reputation and improve overall email deliverability.
- Recipient communication: Encourage affected recipients to check their Google account storage across all services (Gmail, Drive, Photos) and to contact Google support if they believe their mailbox is not full but they are still not receiving emails.
What email marketers say
Email marketers have widely reported a dramatic increase in 'mailbox full' bounces from Gmail accounts since August 2024, causing significant disruptions to their campaigns. Many note that these bounces affect previously engaged subscribers across multiple email service providers and sending infrastructures, highlighting the systemic nature of the issue. The common understanding amongst marketers is that Google has enacted a stricter enforcement of mailbox quotas, leading to a surge in these errors. The challenge for marketers lies in effectively managing these new bounce patterns, particularly when addresses might bounce inconsistently or when the 'mailbox full' error reflects overall Google storage rather than just email capacity. This necessitates a re-evaluation of current bounce handling and suppression strategies to maintain healthy sender reputation and avoid unnecessary hard bounces.
Key opinions
- Shared experience: A consensus among marketers indicates that the issue of elevated 'mailbox full' bounces from Gmail is a shared experience across different sending platforms and IPs.
- Inconsistent bounces: Some marketers observe random impacts, where a user might bounce on one send but receive a subsequent email, making suppression challenging.
- Previous engagement: The affected Gmail addresses were often recently engaged, sometimes just days before they started generating 'mailbox full' bounces.
- ESP limitations: Many ESPs are confirming the trend but haven't provided definitive solutions or explanations, prompting marketers to seek answers elsewhere.
- Google policy shift: The primary hypothesis, later confirmed by some ESPs who contacted Google, is that the increase stems from Google's stricter enforcement of mailbox quotas, which began around August 15th.
Key considerations
- Temporary suppression: Marketers are considering or implementing temporary suppression for 'mailbox full' errors, retrying delivery after a few days, and then permanently suppressing if the issue recurs.
- Segmenting bounces: It is recommended to segment customers based on the 'MailboxFull' bounce type, combined with filters for bounce frequency and engagement metrics, to manage suppression effectively.
- Gmail's unified quota: Understanding that Google's 15GB free storage limit applies across all Google services (Gmail, Drive, Photos) is critical. A user's email inbox might be empty, but their overall Google storage could be full.
- Monitoring engagement: As outlined by WPFunnels in their guide, monitoring engagement is key to identifying potentially problematic addresses before they lead to persistent bounces.
Marketer view
Email marketer from Email Geeks notes an abnormally high bounce rate for 'mailbox full' from Gmail since last Friday, questioning if it's a general trend or an isolated issue.
Marketer view
Email marketer from WPFunnels explains that hard bounces indicate permanent delivery issues with a recipient's address, which can occur when an email address no longer exists.
What the experts say
Email deliverability experts highlight that the recent increase in Gmail 'mailbox full' bounces is likely a result of Google's stricter enforcement of their storage policies, which now encompasses all Google services tied to a user's account. They emphasize the distinction between a deferral (temporary issue) and a hard bounce (permanent failure), noting that many ESPs may be misclassifying these new 'mailbox full' deferrals. Experts advise focusing on the history of bouncing addresses, suggesting that prolonged inactivity or non-email data (like photos or documents) filling up storage could be key factors. They caution against immediate permanent suppression for 'mailbox full' errors, advocating for careful analysis and a nuanced approach to bounce management to avoid mistakenly removing active subscribers. Ultimately, their perspective points to an evolving landscape where senders must adapt to Gmail's consolidated storage limits and refine their bounce handling protocols.
Key opinions
- Data analysis crucial: Experts advise digging into the history of affected addresses to identify patterns and understand why they are suddenly bouncing 'mailbox full'.
- Deferral misclassification: Many of these 'mailbox full' messages, particularly those with 4xx codes within a 5xx response, are actually deferrals being misclassified as hard bounces by ESPs.
- Google's real intent: There's speculation that the 'over quota' error might be wrongly reported by Google's systems or reflects a new, stricter enforcement of their storage limits across all Google services.
- Recipient action: Involving recipients by asking them to open a support ticket with Google is suggested as a way to potentially get information to the right team within Google.
- Underlying storage issues: The data from persistent 'mailbox full' bounces may indicate accounts that are not actively used for email but are filled with other Google Drive data, such as documents or photos.
Key considerations
- Avoid premature suppression: Do not suppress addresses based on a single 'mailbox full' bounce, as it is often a temporary condition. Only permanently suppress for persistent mailbox full errors or 'user unknown' bounces.
- Understand bounce types: Recognize that many 5xy SMTP bounces do not signify an invalid email address and therefore do not require suppression, as discussed in various deliverability guides.
- Monitor delivery patterns: Observe if the pattern of 'mailbox full' bounces continues over time or if the rate decreases as users clear space or are gradually suppressed.
- Verify error messages: Always examine the full rejection message to ensure bounces are correctly categorized and to distinguish between temporary and permanent issues. This aligns with general advice from resources like Spam Resource.
Expert view
Email expert from Email Geeks suggests reviewing the history of email addresses before they started bouncing to identify any patterns or changes in engagement.
Expert view
Deliverability expert from Spam Resource advises that 'mailbox full' is a temporary bounce and senders should retry the address rather than immediately removing it from their list, to avoid losing active subscribers.
What the documentation says
Technical documentation from various sources, including Google's own support pages and SMTP RFCs, provides a foundational understanding of email bounce messages and their implications. The core issue of 'mailbox full' bounces is generally categorized as a soft bounce or transient failure, indicating a temporary condition that should ideally resolve itself with retries. However, the recent spike in Gmail suggests a more rigid application of existing quota rules. Documentation on SMTP error codes distinguishes between temporary failures (4xx) and permanent failures (5xx), which is critical for ESPs and senders to correctly interpret bounce messages. Furthermore, information regarding Google's unified storage policy clarifies that Gmail storage is not isolated but part of a larger ecosystem, where other Google services (Drive, Photos) contribute to the overall quota, potentially leading to 'mailbox full' errors even if the email inbox itself appears empty.
Key findings
- Error code meaning: The 452 4.2.2 SMTP error explicitly states that 'the recipient's inbox is out of storage space,' directing users to Google's support for temporary over-quota issues, as noted in Google's documentation about mailbox quotas.
- Unified storage quota: Google's documentation confirms that all Google services (Gmail, Drive, Photos) contribute to a user's total storage quota, explaining why a user might have an empty email inbox but still receive 'mailbox full' bounces.
- Transient vs. permanent: SMTP standards (RFC 5321) classify 4xx responses as temporary failures, implying that 'mailbox full' errors should be retried. A 5xx indicates a permanent failure that should not be retried.
- Soft bounce characteristics: Documentation generally defines 'mailbox full' as a soft bounce, a temporary issue where the email cannot be delivered immediately but might succeed upon retry, as explained by WPFunnels documentation.
Key considerations
- ESPs bounce handling: Senders should verify their ESP's internal logic for converting deferrals (4xx) into hard bounces (5xx), especially in light of Google's stricter enforcement, to ensure accurate bounce categorization. This is crucial for preventing incorrect suppressions.
- Adhering to RFCs: While Google's behavior is new, standard SMTP protocols (like RFC 5322) still guide fundamental bounce handling. Senders should align their retry policies with these standards, considering 'mailbox full' as transient initially.
- Recipient education: Educational materials from Google highlight the role of users in managing their own storage. Senders might consider advising recipients to check their Google Drive or Photos storage if they experience email delivery issues.
Technical article
Google documentation states that the 'recipient's inbox is out of storage space' and directs users to their support page for temporary over-quota issues, confirming the meaning of the 452 4.2.2 error code.
Technical article
MailBluster documentation describes hard bounces as permanent delivery failures, noting that a consistently full mailbox can eventually lead to a hard bounce classification if left unaddressed.
Related resources
5 resources
Related pages
What causes a sudden spike in email bounce rates, especially from Gmail?
Why is Gmail incorrectly marking emails as bounced due to mailbox quota being full?
Why am I seeing a sudden increase in Gmail 'mailbox full' deferrals?
Why am I seeing bounces for mailbox full followed by opens?
Is mailbox full still a valid email bounce message?
Why am I seeing more Gmail hard bounces today?
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