Summary
The sudden surge in Gmail 'mailbox full' bounces since August 2024 is primarily attributed to Google's stricter enforcement of its 15GB storage limit shared across Gmail, Drive, and Photos, with a possibility of algorithm changes. Prior to this, Gmail seemingly allowed exceeding these limits. This enforcement, combined with users potentially filling their storage faster due to increased uploads and new Google One promotions, has resulted in a spike in bounces. Strategies to mitigate this include employing temporary and permanent suppression techniques, segmenting bounces, monitoring Google Postmaster Tools, ensuring correct email authentication, and verifying accurate bounce message classifications. It's also crucial to investigate the possibility of deferrals being incorrectly classified as hard bounces and to analyze sending practices before the spike for potential contributing factors.
Key findings
- Quota Enforcement: Google is enforcing its 15GB storage limit more strictly since August 2024.
- Shared Storage: The 15GB quota is shared across Gmail, Google Drive, and Google Photos.
- Suppression Essential: Implementing robust suppression strategies is vital to maintain sender reputation.
- Deferral Escalation: ESPs might be translating deferrals (internal message timeout) into hard bounces.
- Legitimate Bounce Codes: Bounce codes 452 4.2.2 and 552 4.2.2 are legitimate indicators of 'out of storage' issues.
Key considerations
- Suppression Strategy: Develop a temporary and permanent suppression strategy based on bounce frequency and engagement.
- Segmentation: Segment recipients based on bounce type and frequency to identify problematic addresses.
- Monitor Postmaster Tools: Use Google Postmaster Tools to track spam rate, domain reputation, and other deliverability metrics.
- Authentication: Ensure SPF, DKIM, and DMARC are correctly configured for email authentication.
- Bounce Verification: Verify that your ESP is accurately classifying bounce messages to avoid misinterpreting other deliverability issues.
- Analyze Sending Practices: Review sending volume, frequency, and list hygiene practices before the August spike.
- Re-engagement Campaigns: Consider launching re-engagement campaigns before permanently suppressing addresses, especially inactive ones.
What email marketers say
12 marketer opinions
The sudden spike in Gmail 'mailbox full' bounces since August 2024 is primarily attributed to Google's stricter enforcement of storage quotas. Previously, Gmail allowed users to exceed their storage limits, but now bounces emails immediately when a user is over quota. This is compounded by factors like users filling storage with photos and documents, potential algorithm changes, and some users not managing their inboxes. Strategies to mitigate this include temporary and permanent suppression of bouncing addresses, segmenting 'mailbox full' bounces, monitoring Google Postmaster Tools, ensuring proper email authentication, and verifying bounce message classifications.
Key opinions
- Quota Enforcement: Google began strictly enforcing storage quotas around August 2024, causing a surge in 'mailbox full' bounces.
- User Behavior: Users filling their storage with data like photos and documents contributes to the issue.
- Suppression is Key: Implementing suppression strategies for addresses with 'mailbox full' bounces is crucial.
- Possible Misclassification: Some ESPs may misclassify other deliverability issues as 'mailbox full' bounces.
Key considerations
- Suppression Strategy: Determine a temporary and permanent suppression strategy for 'mailbox full' bounces.
- Segmentation: Segment your audience to identify users with frequent 'mailbox full' bounces.
- Monitoring Tools: Monitor Google Postmaster Tools for changes in spam rate and domain reputation.
- Re-engagement: Consider a re-engagement campaign before permanently suppressing addresses with mailbox full bounces.
- Authentication: Ensure SPF, DKIM, and DMARC records are configured correctly.
- Bounce Verification: Verify the accuracy of bounce message classifications with your ESP.
Marketer view
Email marketer from Email Vendor Blog shares that the quota enforcement means marketers need to be more aggressive about suppressing inactive users or users who consistently bounce with mailbox full errors to protect sender reputation and ensure deliverability for engaged users.
16 Nov 2023 - Email Vendor Blog
Marketer view
Email marketer from Email Sender Forum recommends ensuring that all email authentication protocols (SPF, DKIM, DMARC) are correctly configured, as deliverability issues can sometimes manifest as increased bounces.
25 May 2023 - Email Sender Forum
What the experts say
4 expert opinions
The sudden increase in Gmail 'mailbox full' bounces around August 2024 points to a complex issue requiring careful investigation and mitigation. The underlying cause may stem from a combination of factors, including deferrals escalated to hard bounces by ESPs, potentially triggered by changes occurring before the observed spike. Effective bounce management, especially for 'mailbox full' bounces, is vital for preserving a good sending reputation. This includes prompt temporary suppression, followed by permanent suppression after multiple failures, and accurate interpretation of bounce codes to ensure legitimate addresses aren't incorrectly removed.
Key opinions
- Bounce Interpretation: ESPs may be translating deferrals (indicated by '[internal] message timeout') into hard bounces.
- Temporal Element: The root cause might predate the observed spike in bounces, suggesting a trigger event earlier in August.
- Strategic Suppression: Implementing temporary suppression, with subsequent permanent suppression upon repeated failures, is a best practice.
- Reputation Impact: Effective bounce management is essential for safeguarding sender reputation.
Key considerations
- Investigate Deferrals: Examine why deferrals are being escalated to hard bounces by your ESP.
- Analyze Prior Changes: Identify any modifications made to sending practices or configurations in the days leading up to the bounce spike.
- Bounce Code Accuracy: Ensure accurate interpretation of bounce codes to prevent unnecessary suppression of valid addresses.
- Temporary Suppression Duration: Determine the optimal duration for temporary suppression before re-attempting delivery.
- Reputation Monitoring: Continuously monitor sender reputation to detect and address any negative impacts from deliverability issues.
Expert view
Expert from Word to the Wise explains that bounce management is crucial for maintaining a good sending reputation. They delve into how to handle both hard and soft bounces effectively, highlighting the importance of correctly interpreting bounce codes and promptly removing problematic addresses from mailing lists, although it does not specify to the increase in bounces in August 2024.
11 Dec 2021 - Word to the Wise
Expert view
Expert from Email Geeks explains that the rejection message containing '[internal] message timeout' indicates a deferral translated into a hard bounce by the ESP. The expert further suggests that the core question is why a large number of recipients ran out of space over the weekend.
28 Mar 2024 - Email Geeks
What the documentation says
4 technical articles
The spike in 'mailbox full' Gmail bounces since August 2024 is largely attributed to Google's potential enforcement of its existing 15 GB storage limit shared across Google Drive, Gmail, and Google Photos. Bounce codes 452 4.2.2 and 552 4.2.2 confirm the legitimacy of these 'out of storage' bounces. Industry documentation emphasizes that 'mailbox full' bounces are soft bounces, suggesting strategies like throttling email volume and allowing retry attempts before classifying them as permanent bounces, especially since inactive accounts often trigger these.
Key findings
- Storage Limit Enforcement: Google may be more actively enforcing the 15GB storage limit across its services (Gmail, Drive, Photos).
- Legitimate Bounce Codes: SMTP error codes 452 4.2.2 and 552 4.2.2 indicate genuine 'out of storage' issues.
- Soft Bounce Nature: 'Mailbox full' bounces are generally considered soft bounces.
Key considerations
- Quota Awareness: Recognize that users have a shared 15GB quota across Google services, not just Gmail.
- Volume Throttling: Consider throttling email volume to allow for potential retry attempts by Gmail.
- Retry Attempts: Allow sufficient time for Gmail to retry delivery before classifying 'mailbox full' bounces as permanent.
- Inactive Account Handling: Recognize that persistent 'mailbox full' bounces may indicate inactive accounts.
Technical article
Documentation from Mailjet explains that mailbox full errors are considered soft bounces. It suggests following best practices such as throttling email volume and allowing ample time for Gmail to retry delivery before classifying the bounce as permanent.
5 Dec 2024 - Mailjet
Technical article
Documentation from Google Developers defines 452 4.2.2 as 'The recipient's mailbox is out of storage space' and 552 4.2.2 'The email account that you tried to reach is over quota'. This confirms that the bounce messages are legitimate.
29 Sep 2022 - Google Developers
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