Summary
A sudden increase in Gmail 'mailbox full' deferrals stems from multiple factors: recipients exceeding storage limits, inactive accounts due to increased spam filtering or general abandonment, and list quality issues like unengaged contacts. While often a soft bounce suggesting a retry, persistent occurrences signal the need for immediate list cleaning, suppression of problematic addresses, and improved engagement strategies. Experts recommend a comprehensive approach encompassing regular list hygiene, robust bounce management with suppression rules, and potentially guiding users on managing their storage.
Key findings
- Storage Exceeded: The primary cause is recipients exceeding their Gmail storage quota (452 error).
- List Decay: Increased 'mailbox full' bounces often indicate list decay and inactive accounts.
- Engagement Impact: Target audience and engagement level directly influence bounce rates.
- Suppression Necessity: Immediate suppression of recipients with persistent 'mailbox full' errors is crucial.
- Transient Nature: The error can be transient, warranting a retry in some cases, but not as a general rule if repeated.
Key considerations
- List Hygiene: Implement a robust list cleaning process to remove unengaged subscribers and inactive accounts.
- Bounce Management: Establish a clear bounce management strategy, including suppression rules and feedback loops.
- Engagement Strategies: Improve engagement strategies to retain active subscribers and prevent account abandonment.
- User Guidance: Consider providing guidance to recipients on managing their Gmail storage.
- Temporary Issues Check: Check for temporary server issues, although list hygiene is the more likely solution.
What email marketers say
10 marketer opinions
A sudden increase in 'mailbox full' deferrals in Gmail can stem from several factors, including recipients exceeding their storage limits, changes in user behavior (like abandoning accounts due to spam), list quality issues (such as stale or unengaged contacts), and potentially temporary server issues. Experts recommend immediate suppression of recipients triggering these errors and advise checking list hygiene, engagement levels, and considering temporary server issues.
Key opinions
- Mailbox Capacity: 'Mailbox full' bounces indicate the recipient's mailbox has reached its storage limit.
- List Hygiene: An increase in these bounces often suggests a need for list cleaning due to stale or unengaged contacts.
- Recipient Behavior: Changes in user behavior, such as abandoning accounts because of spam, contribute to this issue.
- Suppression Importance: Immediately suppress recipients with 'mailbox full' errors to avoid repeated attempts.
- Temporary Issues: Deferrals may also indicate temporary server issues, but this is less common.
Key considerations
- Engagement Levels: Evaluate engagement levels and consider suppressing unengaged contacts.
- List Maintenance: Implement a regular list cleaning process to remove inactive or problematic addresses.
- Bounce Management: Develop a robust bounce management strategy, including immediate suppression of persistent 'mailbox full' bounces.
- Temporary Failures: Consider temporary server issues as a possible cause before immediately suppressing, but prioritize list hygiene if bounces persist.
Marketer view
Email marketer from Email Geeks suggests suppressing unengaged contacts to address full mailboxes.
20 Nov 2024 - Email Geeks
Marketer view
Email marketer from Litmus discusses bounce management, saying a sudden increase in 'mailbox full' bounces could indicate a stale list that needs cleaning, as recipients may have stopped actively using their old accounts.
29 Aug 2023 - Litmus
What the experts say
2 expert opinions
Experts Steve Jones from Spam Resource and Laura Atkins from Word to the Wise attribute a sudden increase in 'mailbox full' bounces to issues with list quality and decay. Both emphasize the importance of immediate list cleaning and hygiene practices, including setting up suppression rules and removing unengaged subscribers, to address the problem effectively.
Key opinions
- List Decay: Increased 'mailbox full' bounces indicate the list is likely decaying.
- Inadequate Maintenance: The problem arises when email addresses aren't being actively maintained by recipients.
- Suppression Rules: Implementing suppression rules is crucial to prevent further sending to problematic addresses.
Key considerations
- Immediate Action: Address the issue promptly through list cleaning and engagement evaluation.
- List Hygiene Practices: Emphasize regular list hygiene activities, such as removing unengaged subscribers.
Expert view
Expert from Spam Resource, Steve Jones, discusses bounce management strategies, noting that a spike in 'mailbox full' bounces often suggests that your list needs immediate attention and cleaning because these addresses aren't actively maintained, or the mailbox is full. He recommends having suppression rules to ensure these email addresses don't receive more email from you.
2 Jul 2024 - Spam Resource
Expert view
Expert from Word to the Wise, Laura Atkins, responds to a question about dealing with email engagement issues, she mentions that a sudden increase in mailbox full bounces could be an indicator of list decay. She recommends using list hygiene practices, such as removing unengaged subscribers.
12 Aug 2021 - Word to the Wise
What the documentation says
3 technical articles
Documentation from Google, RFC 5321, and AWS indicates that a 'mailbox full' deferral, often accompanied by a 452 error, primarily occurs when a recipient's mailbox exceeds its storage quota or they aren't actively checking their email. While RFC 5321 suggests retrying delivery due to the transient nature of the error, AWS emphasizes implementing a feedback loop and suppressing hard bounces to improve deliverability.
Key findings
- Storage Limit: The recipient has exceeded their email storage limit.
- Transient Error: RFC 5321 designates this as a transient failure (4xx error), suggesting retries are appropriate.
- Inactivity: Recipients may not be regularly checking their email, leading to full mailboxes.
Key considerations
- Initial Retry: Consider an initial retry, given the transient nature of the error.
- Feedback Loop: Implement a feedback loop to identify and manage bounces effectively.
- Hard Bounce Suppression: Suppress hard bounces and persistent 'mailbox full' bounces to maintain deliverability.
- User Guidance: As Google recommends, directing users to support articles on managing storage may be helpful.
Technical article
Documentation from Google Support explains that a 452 error related to insufficient mailbox space means the user has exceeded their storage quota. Direct users to the support article on managing storage.
19 Nov 2022 - Google Support
Technical article
Documentation from RFC 5321 (SMTP standard) describes that 4xx error codes indicate transient failures, like a full mailbox. The sending system should retry delivery later.
2 Apr 2025 - RFC 5321
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