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Mailbox Full: What to Check Before Deleting Emails

If new emails stop arriving, first check the bounce code returned to the sender and the mailbox quota. We examine a safe sequence of actions that avoids deleting necessary correspondence and accidentally changing DNS settings.

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A woman checks a full office mailbox before safe cleanup
In this article

If new emails stop arriving, do not start by mass-deleting messages or changing DNS settings. Ask the sender to provide a full delivery status notification (DSN), locate the extended status code, and simultaneously check the mailbox quota in the hosting control panel. The code X.2.2 indicates a full mailbox; X.3.1 indicates insufficient space in the mail system, which an individual mailbox owner may not be able to fix alone. These values are defined in RFC 3463. The result of the check is not a vanished warning, but a successfully received control email without a new rejection and available free space in the control panel.

What Exactly Could Have Filled Up

Indicator

What it means

Who typically resolves it

X.2.2 Mailbox full

The quota or physical capacity of the specific mailbox has been exceeded

Mailbox owner or domain administrator

X.3.1 Mail system full

Destination mail system storage exhausted

Mail system administrator or provider

X.2.3 Message length exceeds limit

The size of a single message exceeds the limit set for this mailbox. This is not a general storage quota.

The sender reduces the message size or the recipient changes the limit

X.2.1 Mailbox disabled

The mailbox exists but does not accept messages

The administrator checks the account status

The first digit of the extended code indicates the response class: 4 means a temporary failure; 5 means a permanent failure. With a permanent failure, simply resending usually does not help; the message content must be changed or the cause of the failure must be resolved on the recipient's side. RFC 3463 recommends treating mailbox overflow as a temporary error. A real report may contain a temporary code 4.2.2 or a permanent one 5.2.2; the latter is shown in the cPanel documentation example. Preserve the actual report code: pair 2.2 indicates a mailbox overflow, while the first digit determines the failure class. Do not confuse this with the size of a single message or a disabled account.

First, Read the Bounce Message

A delivery failure report is more useful than a retelling of 'the mail is not working.' Ask the sender to forward it as an attachment or share the technical details through an authorized channel, without publishing customer addresses or correspondence content. Record:

  • recipient address and the exact time of the attempt;

  • extended code of the form 4.2.2 or 5.2.2;

  • text of the recipient server's response;

  • message identifier, if provided;

  • the external mailbox from which the check was performed.

If the sender did not receive a failure notice, this does not prove the mailbox is working: the message might still be in the queue or accepted and then filtered. Conversely, code X.2.2 already provides a specific reason; at this point, checking SPF, DKIM, or changing MX records will not free up space.

Verify the Quota in the Hosting Panel

  1. Open exactly the mailbox specified in the rejection message and record its current volume and assigned quota.

  2. Check the account's total disk limit or mailbox space: a website's free space does not always equal available mailbox space.

  3. Review the volume distribution across folders—Inbox, Sent, Drafts, Spam, and Trash may be counted differently.

  4. Locate large and old messages, but do not delete anything until you have saved the necessary correspondence and verified retention policies.

  5. If the entire mail system is full rather than a single mailbox, or if the panel indicator is unclear, provide the provider with the address, time, error code, and message identifier.

In the cPanel documentation for mailbox management, the current volume and quota are displayed separately, and the Email Disk Usage section breaks down usage by folder. This is an example of a specific control panel, not a universal button name. The documentation also warns that values may update with a delay due to caching: after cleaning, do not declare the issue resolved simply because the number has not yet changed or, conversely, has disappeared instantly.

Free Up Space Without Losing Necessary Correspondence

  • First, save messages required for orders, financial settlements, warranties, or internal audits.

  • Start with known large attachments and unnecessary copies, not with a 'delete everything' command.

  • Check whether deletion frees space immediately and whether you need to empty the trash separately in your system.

  • Do not mix mailbox cleanup with DNS changes, password updates, or mail routing changes: these are different actions with different risks.

  • If emails must be retained per company internal policy, coordinate archiving before deletion.

There is a nuance: a button with the same name can perform very different actions. In Plesk Obsidian, the Empty mailbox command deletes incoming, outgoing, and draft messages for the selected mailbox. This is not a careful cleanup of large attachments but a complete emptying. For a store's working address, this operation must not be used blindly.

How to confirm that delivery has been restored

  1. Wait until the panel shows the available free space, accounting for possible recalculation delays.

  2. Send a single test email from an external service to the address being checked. Use a unique subject line and neutral content without customer data.

  3. Verify that the sender did not receive a new error and that the email appeared in the expected mailbox.

  4. After receiving the control email, record again how much space the messages in the mailbox currently occupy and the delivery time. This refers to the actually used volume, not the allocated storage limit.

  5. If this is an address for orders, separately perform the allowed test of the store's standard notification: a manual email does not prove the site is working.

The control email does not have to follow the same route as the online store notification. If an external test arrives but the order email does not, only the receipt of that control message is confirmed. Between the control email and the notification, the mailbox could have filled up again. Additionally, filtering or exceeding the allowed size of another message is possible. Next, compare the time, sender, size, and recipient response for both messages, then verify the notification route. The article «Order Email Path from Store to Inbox» will help continue the chain verification: it separates notification creation, handover to the mail service, and the recipient system's response.

When the cause is not a quota

Observation

Likely direction of the check

X.2.3 or X.3.4

The size of a specific email exceeds the limit

X.2.1

The mailbox is disabled or temporarily not accepting mail

X.3.2

The recipient's mail server is currently not accepting messages over the network

The message was accepted, but it is not in the inbox

Spam, quarantine, user rule, or another folder

The store did not create a message

Event, template, queue, or site integration

Checking the MX record is relevant when the failure indicates a domain, route, or mail server unavailability, rather than after a confirmed X.2.2. To check records individually, open the DNS record checking service, but its result does not show the mailbox quota usage.

What result to consider sufficient

The cause is confirmed when the rejection code aligns with the quota indicator for a specific mailbox or the entire system. Restoration is confirmed when, after safe cleanup or an agreed limit increase, the panel shows available space, new external messages are accepted without rejection, and they appear in the recipient's inbox. For a store address, an additional separate result is required: a standard notification is generated by the site and traverses the entire route. Information and documentation were verified on November 2, 2026. Section names and the sequence of actions depend on the panel and provider; disputed codes should be forwarded to support along with the timestamp and message identifier.

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