552 5.2.2: The mailbox is full (or, in Microsoft 365, the sender is over quota)

At a glance

• Type: permanent failure (class 5, RFC 3463 §2). The sending server does not retry; sending the same message again fails the same way until the cause is fixed.
• Basic code 552: “Requested mail action aborted: exceeded storage allocation” (RFC 5321 §4.2.3).
• Enhanced code 5.2.2: “Mailbox full” in the IANA registry (RFC 3463), in the group mailbox status (RFC 3463 §3.3).

Most of the time this means the recipient's mailbox is full and the server has given up on it. In Microsoft 365, a 5.2.2 can also mean the opposite side is the problem: you, the sender, went over your sending limits.

What it means

The basic code 552 says the action was aborted because a storage allocation was exceeded (RFC 5321 §4.2.3). RFC 3463 §3.3 defines X.2.2 as "mailbox full" and says it should be used as a persistent transient failure, since the owner can delete messages. A server that sends it with the permanent 552 has decided not to wait; Gmail, for example, does so when the full mailbox is also inactive. The temporary form is 452 4.2.2.

One more detail: old SMTP software used 552 for "too many recipients". RFC 5321 §4.5.3.1.10 says the correct code for that is 452, and that clients should treat a 552 in that case as temporary.

Which one you have

Read whose mailbox the bounce talks about.

• Recipient mailbox full. The bounce names the recipient and mentions storage or quota. Gmail returns 552 5.2.2 when the inbox is out of storage space and the account is inactive (Google's SMTP error reference).
• Sender over quota (Microsoft 365). The NDR comes from your own Microsoft 365 organization and says the submission quota was exceeded. Microsoft uses 5.2.2 when an account passes its recipient or message rate limits, and lists a limit of 10,000 recipients per day per account (Exchange Online NDR reference).

Common causes

• A mailbox nobody reads any more, filled to its limit.
• Large attachments that use up the last of a recipient's quota.
• In Microsoft 365: a mass mailing sent from a normal user mailbox.
• In Microsoft 365: a compromised account sending spam, which also pushes it over the limits.

How to fix it

If the recipient's mailbox is full:

1. Contact the person another way if the message matters.
2. Send smaller messages and share large files as links.

If you are over the Microsoft 365 submission quota:

1. Wait for the limit window to pass before sending again.
2. Check the account's sent items for mail you did not send. If you find any, secure the account first.
3. Move newsletters and bulk sends to a service meant for bulk mail instead of a user mailbox.

What to do with the address

For a recipient mailbox that is full and inactive, suppress the address: Gmail has told you nobody is using it. For a Microsoft quota NDR, the recipient addresses are fine; resend once your account is under its limits again.

Related codes

• 452 4.2.2: The mailbox is full
• 550 5.2.1: The mailbox is disabled and takes no mail
• 550 5.4.5: The sender reached a daily sending limit (Google)
• 552 5.3.4: The message is too big

See every bounce code in the dictionary.

Many bounces from addresses that do not exist can be avoided: check an address with our free email checker, or clean a whole list before you send.

How we wrote this: drafted by the email-validation.org team with the help of AI writing tools, from our product documentation and the sources linked in the text.