Summary
A 'mailbox full' bounce occurs when a recipient exceeds their storage quota, often due to shared storage models like Gmail. These are soft bounces, meaning the email address remains valid, and future delivery attempts may succeed. Research suggests that around 20% of mailboxes generating this bounce engage with another email within a week, with over 50% becoming active again within a few months. While retrying is acceptable, persistently sending to full mailboxes can harm sender reputation. Effective management includes using feedback loops (FBLs) instead of solely relying on bounce messages, careful handling of suppressed addresses, and implementing a system to remove addresses after multiple soft bounces.
Key findings
- Cause: Recipients exceeding storage quota.
- Soft Bounce: Classified as a soft bounce; email address remains valid.
- Engagement: About 20% engage with other emails within a week.
- Recovery: Over 50% become active again within a few months.
- Risk: Persistently sending harms sender reputation.
- Gmail specific: Gmail shared storage can trigger full mailboxes
Key considerations
- Retry: Consider a cooldown period before retrying.
- FBLs: Utilize Feedback Loops (FBLs) for bounce management.
- Suppression: Manage suppressed addresses carefully.
- Removal: Remove addresses after multiple soft bounces.
- Proactive Processing: Implement proper bounce processing.
- Storage: Storage quotas prevent excessive database growth.
What email marketers say
9 marketer opinions
A 'mailbox full' bounce is categorized as a soft bounce, meaning the recipient's mailbox has exceeded its storage limit, but the email address remains valid. While future delivery attempts may succeed, repeatedly sending to full mailboxes can negatively impact sender reputation. Data indicates that roughly 20% of mailboxes that trigger this bounce engage with other emails within a week. It is recommended to wait a week before retrying and to implement a system to manage bouncebacks, including removing addresses after multiple soft bounces to avoid deliverability issues.
Key opinions
- Soft Bounce: 'Mailbox full' is a soft bounce indicating the recipient's inbox is over capacity.
- Temporary Issue: It's a temporary issue, and future delivery attempts might succeed.
- Engagement Rate: Around 20% of mailboxes that bounce due to being full engage with emails within a week.
- Sender Reputation: Repeatedly sending to full inboxes can negatively impact sender reputation.
Key considerations
- Retry Strategy: Consider waiting a week before retrying after a 'mailbox full' bounce.
- Bounce Management: Implement a system to manage bouncebacks and remove addresses after multiple soft bounces.
- List Hygiene: Maintain a clean email list to improve deliverability and sender reputation.
- Monitoring: Monitor bounce rates to maintain a healthy sender reputation.
Marketer view
Email marketer from HubSpot says that to improve email deliverability, it's important to clean up your email list by removing invalid or inactive addresses. While 'mailbox full' is a soft bounce, continuously sending to these addresses can hurt your sender reputation.
11 Sep 2024 - HubSpot
Marketer view
Email marketer from WebHostingTalk Forum explains that handling bouncebacks is important. While 'mailbox full' is temporary, persistently sending to these addresses can get you blacklisted. They recommend implementing a system to automatically remove addresses after a certain number of soft bounces.
1 May 2022 - WebHostingTalk Forum
What the experts say
4 expert opinions
Full mailbox bounces are often caused by users exceeding their storage limits, especially on platforms like Gmail where storage is shared across multiple services. These bounces are not permanent failures; resending emails after a cooldown period can be effective, with a significant portion of mailboxes becoming active again within a few months. Proper bounce processing is crucial, and using feedback loops (FBLs) is recommended over relying solely on bounce messages. Careful management of suppressed addresses is also important to avoid harming sender reputation and increasing the likelihood of emails being marked as spam.
Key opinions
- Gmail Storage: Gmail's shared storage model contributes to frequent quota limits.
- Temporary Failure: Mailbox full bounces are not permanent failures.
- Recovery Rate: Over 50% of full mailboxes become active again within a few months.
- Bounce Processing: Proper bounce processing is crucial for deliverability.
- FBLs: Feedback Loops (FBLs) are superior to bounce messages for issue identification.
- Suppressed Addresses: Careful suppression management prevents spam folder placement.
Key considerations
- Cooldown Period: Implement a cooldown period before resending to bouncing addresses.
- Feedback Loops: Utilize Feedback Loops (FBLs) to manage deliverability.
- Sender Reputation: Prioritize sender reputation through strategic suppression management.
Expert view
Expert from Email Geeks explains that Gmail shares storage with photos and other files, which means accounts can reach their quota limit and be cleaned up more frequently than expected for a standard email account.
5 Sep 2024 - Email Geeks
Expert view
Expert from Email Geeks explains that a mailbox full bounce is not a permanent failure, and resending emails after a short cooldown period is a viable strategy, with data suggesting that over 50% of such mailboxes become active again within a few months.
17 Oct 2023 - Email Geeks
What the documentation says
4 technical articles
Documentation from various sources indicates that 'mailbox full' bounces are caused by recipients exceeding their allocated mailbox quota, often implemented to prevent database growth. These bounces are classified as soft or transient failures, meaning the email address is still valid, and future delivery attempts are acceptable after a period of time.
Key findings
- Quota Limits: Mailbox quotas in systems like Exchange Server trigger 'mailbox full' bounces.
- Database Growth: Quotas prevent excessive database growth.
- Soft Bounce: 'Mailbox full' is classified as a soft or transient bounce.
- Retry Acceptable: Retrying delivery after some time is acceptable.
- Valid Address: The email address remains valid, but the mailbox needs to free up space.
Key considerations
- Retry Strategy: Consider a retry strategy to attempt delivery at a later time.
- Delivery Attempts: Future delivery attempts may succeed once space is available.
Technical article
Documentation from SparkPost shares that 'mailbox full' is considered a soft bounce because the email address is valid and accepting mail, but the recipient needs to free up space. Messages to full mailboxes can be retried.
9 Oct 2022 - SparkPost
Technical article
Documentation from Microsoft Learn explains that Exchange Server quotas limit mailbox size to prevent excessive database growth. When a user exceeds their quota, the server rejects new messages, resulting in a bounce back to the sender, commonly a 'mailbox full' error.
19 Sep 2023 - Microsoft Learn
Can a hard bounced email address become deliverable again, and under what circumstances?
Can Gmail give false positive SMTP bounce responses?
How are email bounce rates calculated and what is considered a good bounce rate?
How do Gmail 'mailbox full' bounces affect email deliverability and how can I monitor it?
How should email marketers handle 452 mailbox full bounce codes, especially from Gmail, during email warmup?
How should email marketers handle permanent bounce errors like full or inactive mailboxes?
