A “mailbox full” message does not always mean that the same storage limit has been reached. It may refer to the server mailbox quota, storage used by the email app on your device, an attachment size limit, or temporary provider throttling. Identifying the limit first helps you choose the right fix.
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What “mailbox full” can mean
Server mailbox quota: Your mail provider limits the amount of email data stored on the server. When this quota is reached, new messages may not be accepted and sending or receiving can fail. Deleting messages from a third-party client helps only when the deletion is synchronized with the server.
Local client storage: An email client may also store downloaded messages, attachments, and other data on your computer or mobile device. A local storage problem affects the app or device, even when the server mailbox still has available space. Deleting a message in the client may not free local space immediately if the app keeps a local copy or cached data.
Attachment size limit: A message can be rejected because its attachment is too large. This is separate from the total amount of email stored in the mailbox. Deleting older messages will not make an oversized attachment smaller.
Provider throttling: A provider may temporarily restrict sending or receiving activity. This can look like a general email failure, but deleting messages does not remove a temporary sending restriction. SMTP error codes can help identify why a message was not delivered. See SMTP error codes and their meaning for an explanation of these server responses.
How to check the server mailbox quota
Start with the mailbox itself, not only the error shown by the email app. Sign in to webmail or the mybox dashboard and open the email or mailbox area. The mybox Email section is used to monitor resource usage and manage mailboxes.
- Open the mailbox or Email section.
- Look for storage usage, quota, or mailbox size information.
- Compare the used space with the mailbox limit.
- Check folders that may contain large amounts of data, including the inbox, sent mail, and trash.
If the server shows that the mailbox is full, the email client is reporting a server-side condition. Changing the client settings alone will not increase the mailbox quota.
How to check local storage in the email client
Open the affected email client and review its account, storage, or data-file settings. Check how much space the app uses on the device and whether it downloads full messages or attachments for offline use. The exact setting name depends on the client.
If the server quota has available space but the client still reports a full mailbox, compare the error in webmail with the error in the app. A problem that appears only in the app is more likely to involve local storage, synchronization, or the client’s data file than the server quota.
Safe ways to free mailbox space
- Find large messages. Review messages with large attachments first. Remove messages that are no longer needed.
- Review Sent mail. Sent messages can include copies of large attachments and may use significant mailbox space.
- Empty the trash. Moving messages to Trash may not free the quota while those messages remain there. Permanently remove them if the mailbox interface provides that option.
- Archive selectively. Archive messages when the archive remains within the same mailbox quota. Archiving is useful for organising mail, but it does not reduce server storage if the archived messages are still stored in that mailbox.
- Allow synchronization to finish. When deletion is made in a third-party client, wait for the client to synchronize with the server, then check the quota again in webmail or the mybox dashboard.
For a broader storage review, the mybox mailbox storage audit covers auditing, archiving, and deleting old data.
What deleting messages can and cannot fix
| Cause | Can deleting mailbox messages help? | What to check |
|---|---|---|
| Server mailbox quota reached | Yes, if deletion is synchronized and trash is emptied. | Quota usage in webmail or the mybox Email section. |
| Local client storage full | Sometimes. The app may retain cached data. | Storage and data-file settings on the device. |
| Attachment too large | No. | Reduce the attachment or send it by another supported method. |
| Provider throttling | No. | Review the returned SMTP error and provider status. |
When to contact the mail provider
Contact the mail provider when the server quota is not full but webmail and the third-party client both fail, when the quota does not change after synchronized deletion and trash removal, or when the returned SMTP response indicates a provider-side restriction. Include the exact error message and SMTP code when one is shown. This gives support a clear starting point for checking the mailbox and delivery status.