Mailbox Full or Over Quota (552 5.2.2, 452 4.2.2): What the Bounce Means and What to Do

A "mailbox full" bounce is one of the easiest to understand and one of the most mishandled. Your message was fine, the address exists and the server was willing to accept the mail, but the recipient has used up the storage assigned to their account, so the server cannot store one more message. The bounce may read 552 5.2.2 The email account that you tried to reach is over quota, 552 5.2.2 Mailbox full, 452 4.2.2 Over quota, 554 5.2.2 Mailbox full or, on some systems, 550 5.2.2 Quota exceeded. The codes differ, and the difference tells you whether to retry. This guide explains the codes, what a sender should do in each case, what a mailbox owner can do in minutes to fix the problem, how the provider limits usually work and how a mailing list should treat addresses that keep reporting that they are full.

What the code means

Enhanced status codes, defined in RFC 3463, have three numbers. The second number, 2, means "mailbox status", and the third, 2, means "mailbox full". The first number says whether the failure is permanent (5) or temporary (4). So 4.2.2 is "mailbox full, try again later", and 5.2.2 is "mailbox full, do not try again". In practice, servers choose between them according to policy. A system that expects owners to clean up quickly returns the temporary form and keeps your message in your queue, and a system that prefers to inform the sender immediately returns the permanent form and lets you decide. Either way the basic fact is the same: there is no room.

What a sender should do

When you get a temporary 4.2.2

Your mail system will keep the message and retry on its schedule. You do not need to do anything, though if the message is time-sensitive, contact the person by another channel and tell them their mailbox is full. After a number of days, normally four or five in a default configuration, the mail system gives up and sends you a final bounce. Understand that a long retry may not help: mailbox owners often notice the problem only when someone calls them. See queued and deferred email for how the queue works.

When you get a permanent 5.2.2

The message was not delivered and will not be retried. Resend it later, once the recipient has had time to free space, or send a short message by another route asking them to clear their mailbox. Do not resend repeatedly: each failure counts as a delivery failure in your logs, and repeated attempts to a full mailbox annoy the recipient's provider. If the message was important, such as a signed document or a payment receipt, use another channel and keep a record.

What not to do

• Do not resend every few minutes. It cannot succeed until the owner acts.
• Do not treat the address as invalid. The mailbox exists, and a person may still want your mail.
• Do not split a large attachment into many small messages. You may fill the box faster, and you will create a poor experience. Check the limits in attachment size limits and share a link instead.
• Do not guess that the recipient is ignoring you. Many people do not know their mailbox is full.

What the mailbox owner can do

If you are the person whose mailbox is full, the fix is usually quick. The steps depend on the provider, but the pattern is the same.

1. Find out the quota and how much you use. Most providers show it in the account settings or at the bottom of the mailbox.
2. Empty the spam and trash folders. In many services these count toward the quota, and they are often the largest folders.
3. Sort by size and delete or download the largest messages, especially those with attachments. Save important attachments to a drive or storage service.
4. Search for old newsletters and notifications, then delete them in bulk, and unsubscribe from the sources you no longer need.
5. Archive old mail to a local file or a separate archive mailbox if your provider supports it.
6. If the account is shared storage, check whether files or photos in the same account are using the space. Many providers share one quota across mail, files and photos.
7. If you need more room permanently, upgrade the plan or ask the administrator to raise your quota.

After you free space, mail does not appear instantly in every case. Messages that your sender's system is still retrying arrive on the next attempt, which can be minutes or hours away. Messages that were permanently rejected must be sent again; ask the sender to resend them. For an organisation, the administrator can check the mailbox size and quota in the admin console or with the server's management tools, and can send a warning automatically at 80 or 90 percent of the quota so that users act before the box fills.

Where the limit comes from

Quotas are set by the provider or the organisation, and they differ widely. Free consumer accounts usually share a fixed amount of storage between mail and other services. Business accounts set a quota per mailbox and may allow larger values on higher plans. Hosting companies apply a per-account or per-domain quota in the control panel; when the whole hosting account is full, every mailbox on it can bounce, even if each looks small. Some systems also apply a limit on the number of messages, on folder size or on the size of one message, which produce related errors. If the bounce says the message is too big, not that the mailbox is full, see email size limits and MIME overhead.

Related errors that look similar

Handling full mailboxes in a mailing list

List senders need a clear rule. A single mailbox-full bounce tells you little: people go on holiday, forget to clean up or get a new job. Do not suppress the address after one occurrence. Retry at the next send, but if the same address reports a full mailbox on three or four sends in a row over a month or more, treat the address as inactive and move it out of regular campaigns. A mailbox that stays full for months is usually abandoned, and abandoned addresses are among the places where providers keep spam traps. For the reasoning and the practice, see spam traps and honeypots, list hygiene and sunset policies and suppression list management.

Make sure your platform classifies these correctly. A good system records mailbox-full as a soft bounce, a category that counts toward suppression only after repeated occurrences, whereas user-unknown is a hard bounce that suppresses immediately. The difference is explained in hard and soft bounces. Check your reports for a rising number of mailbox-full bounces: a spike at one domain can mean that its provider lowered quotas or that a hosting account filled up, and is worth a message to the domain's administrator.

For hosts and administrators

If you run mail for others, set alerts well before mailboxes fill, show usage in a visible place and consider an automatic message to the user at 90 percent. Think about what the server does when it is full: returning a temporary code gives the user time to react without losing mail, while a permanent code loses the message but tells the sender at once. Whichever you choose, make it consistent, and write the explanation in the bounce text in plain words, such as "The recipient's mailbox is full. Please try again later or contact them another way." A clear message prevents confusion and support tickets on both sides.

References and further reading

• RFC 3463: Enhanced Mail System Status Codes
• RFC 5321: Simple Mail Transfer Protocol
• IANA: Enhanced Status Codes registry