Summary
Experts, marketers, and technical documentation widely agree that 'mailbox full' is still a valid bounce message, although less frequent than in the past. It typically results from exceeding mailbox quotas, often due to storage of large files like photos and videos, particularly in services like Gmail and iCloud. While some consider it a hard bounce, a common recommendation is to treat it as a soft bounce initially and retry delivery over a few days before classifying it as a permanent failure. Factors contributing to this issue include abandoned accounts, corporate environments with strict storage policies, and older email systems. Technical documentation highlights that mailbox quotas are enforced by systems like Exchange Server, cPanel, and Exim, and that RFC 3463 defines 'mailbox full' as a permanent failure condition.
Key findings
- Validity: 'Mailbox full' remains a valid bounce message.
- Decreasing Frequency: The frequency of 'mailbox full' bounces has decreased due to increased storage capacities, but it still occurs.
- Quota Exceedance: The primary cause is exceeding storage quotas, often due to large files like photos and videos, especially in Gmail and iCloud.
- Hard vs. Soft Bounce: Opinions vary on whether it's a hard bounce (permanent failure) or a soft bounce (temporary issue), but initial soft bounce treatment is often recommended.
- Contributing Factors: Other contributing factors include abandoned mailboxes, corporate environments with strict storage policies, and older email systems.
- Technical Standards: RFC 3463 defines 'mailbox full' as a permanent failure condition (5.2.2).
- Platform Specific: Gmail and iCloud are mentioned, along with Exchange, cPanel and Exim.
Key considerations
- Bounce Handling: Implement a bounce handling strategy that initially treats 'mailbox full' as a soft bounce and retries delivery before classifying it as a hard bounce, usually over a period of days.
- Data Hygiene: Regularly clean email lists to remove addresses consistently returning 'mailbox full' errors.
- Quota Management: Email administrators should effectively manage mailbox quotas and communicate storage policies to users.
- User Education: Inform users about storage limits and how to manage their mailbox size.
- Alternative Storage: Consider the use of cloud-based storage services, such as Google Drive and iCloud Photos, which share quota space with email inboxes, impacting available email storage.
- Transient Error: The Mailbox Full error code is a transient (temporary) error for a transient condition.
What email marketers say
15 marketer opinions
The consensus among email marketers is that 'mailbox full' is still a valid bounce message, although its frequency has decreased due to increased storage capacities. It often occurs when users exceed storage quotas by storing large files such as photos and videos, especially in Gmail and iCloud. While some consider it a hard bounce, others advise treating it as a soft bounce initially, retrying delivery before classifying it as a permanent failure. Abandoned mailboxes and corporate environments with strict storage policies are also contributing factors.
Key opinions
- Validity: 'Mailbox full' is still a valid bounce message.
- Frequency: The occurrence of 'mailbox full' bounces has decreased due to increased storage capacities.
- Storage Usage: Exceeding storage quotas is often due to storing large files such as photos and videos (e.g., in Gmail and iCloud).
- Contributing Factors: Other factors include abandoned mailboxes and corporate environments with strict storage policies.
- Bounce Classification: Opinions vary on whether it's a hard bounce (permanent failure) or a soft bounce (temporary issue).
Key considerations
- Storage limits: Be aware that mailbox storage is often shared with other storage platforms like Google Drive and Photos, and that even though individual mail storage is often high it can quickly fill up due to these other systems.
- Bounce Handling: Consider treating 'mailbox full' bounces as soft bounces initially and retrying delivery before classifying them as hard bounces.
- Data Hygiene: Implement data hygiene practices to remove addresses that consistently return 'mailbox full' errors.
- Storage Policies: Be aware that depending on your sender reputation you may be temporarily blocked if sending to a mailbox at the point it reaches full, regardless of the storage policy of the target mailbox.
- Abandoned Accounts: Recognize that a 'mailbox full' bounce may also indicate an abandoned account.
Marketer view
Email marketer from Mailjet indicates that 'mailbox full' is classified as a hard bounce, meaning that it is a permanent error. They suggest that this error means a recipient's mailbox has reached its storage limit.
5 Jan 2022 - Mailjet
Marketer view
Email marketer from Webmaster Forum states that while 'mailbox full' bounces are less frequent than in the past, they still exist. Especially in corporate environments with strict storage policies or older email systems.
24 Oct 2023 - Webmaster Forum
What the experts say
3 expert opinions
Experts agree that 'mailbox full' is still a valid bounce code, indicating the recipient's inbox is over capacity. The recommended approach is to initially treat it as a soft bounce and retry delivery over a few days. If the issue persists, it should then be classified as a hard bounce, suggesting a more permanent problem like an abandoned account or continued storage overload.
Key opinions
- Validity Confirmed: 'Mailbox full' remains a valid bounce code.
- Initial Soft Bounce: The recommended initial action is to treat the bounce as a soft bounce and retry delivery.
- Retry Period: Retry delivery over a period of a few days.
- Hard Bounce Escalation: If the bounce persists, escalate it to a hard bounce.
- Possible Causes: Persistent 'mailbox full' errors may indicate an abandoned account or continued storage overload.
Key considerations
- Bounce Handling Strategy: Implement a bounce handling strategy that initially treats 'mailbox full' as a soft bounce and retries delivery.
- Persistence: If the 'mailbox full' error persists after several retries, consider it a more permanent issue and take appropriate action (e.g., removing the address from your list).
- Possible Reasons: Consider that the error might be due to the recipient's account being truly full or possibly abandoned.
Expert view
Expert from Word to the Wise explains in an article about handling bounces that 'user or mailbox is full' errors should be treated as a soft bounce initially, retrying delivery. If the bounce persists, it should then be treated as a hard bounce, indicating a permanent issue with the address.
21 Dec 2021 - Word to the Wise
Expert view
Expert from Email Geeks advises retrying delivery to "mailbox full" addresses over a few days, as active users may clear the backlog. If the issue persists, it is likely an abandoned account or used for photo/video storage.
30 Sep 2021 - Email Geeks
What the documentation says
4 technical articles
Technical documentation confirms that 'mailbox full' is a valid bounce message resulting from exceeded mailbox quotas. Exchange Server, cPanel, and Exim enforce quotas, preventing email delivery when limits are reached. RFC 3463 defines 'mailbox full' as a permanent failure condition indicated by a specific status code.
Key findings
- Valid Bounce: 'Mailbox full' is a valid bounce message.
- Quota Enforcement: Mailbox quotas are enforced by Exchange Server, cPanel, and Exim.
- Delivery Failure: Exceeding the quota prevents email delivery.
- Permanent Failure: RFC 3463 defines 'mailbox full' as a permanent failure condition with specific status code.
- Status Code: The code for 'mailbox full' is 5.2.2 according to RFC3463
Key considerations
- Quota Management: Administrators should effectively manage mailbox quotas to avoid delivery failures.
- User Awareness: Users should be informed about quota limits and how to manage their mailbox size.
- Bounce Handling: Email systems should handle 'mailbox full' bounces appropriately, potentially with retry mechanisms before marking as permanent failure.
Technical article
Documentation from Microsoft Support explains that Exchange Server uses mailbox quotas to control mailbox size. When a mailbox exceeds its quota, users may be unable to send or receive new email, leading to a 'mailbox full' bounce message for senders. Quotas are configured at the database or mailbox level.
13 Dec 2024 - Microsoft Support
Technical article
Documentation from Exim states that a "Mailbox Full" error is a still a valid bounce message. This often occurs when a quota is enforced on the user account at the system level and the user has exceeded this quota.
24 Oct 2022 - Exim
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