5.2.0: mailbox problem, unspecified
The recipient's mailbox exists, but something about it stopped the delivery and the receiving server did not say what.
- Standard
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 5.2.0
- Provider
- Standard SMTP codes
- Temporary or permanent
- PermanentRefused for good: the message comes back to the sender, and resending it gets the same answer.
- Who has to act
- Either side, depending on the cause. Start with the checks below that are yours.
- What the server says
5.2.0 Other or undefined mailbox status
What it means
X.2.x codes are about the mailbox itself, which RFC 3463 places under the general control of the recipient. With detail 0, the server confirms the mailbox exists but gives no specific reason: it could be a storage error, a delivery rule, a locked or migrating mailbox, or a local policy. 5.2.0 means the server gave up on this message and returned it. A 4.2.0 means the mailbox is expected to become usable again, and the sending server keeps retrying until it succeeds or its retry period runs out.
Common causes
- A storage or database error on the mailbox server while writing the message.
- A mailbox that is locked, being moved, or held by a rule on the recipient's side.
- A local delivery rule or filter that failed without a code of its own.
How to fix it
- 01Read the text after the code; servers often add the real reason there.
- 02For 4.2.0, wait for the retries before doing anything.
- 03If 5.2.0 repeats, tell the recipient by another channel so their administrator can check the mailbox.
- 04Recipient admins: search the mailbox server's delivery logs for the message ID in the bounce.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
Related codes
- 5.2.1Mailbox disabled.The recipient's mailbox exists but has been switched off and is refusing messages, for a while or for good depending on the class of the code.
- 5.2.2Mailbox full.The recipient's mailbox has reached its storage quota, so the server will not take more mail until the owner deletes messages or gets more space.
5.2.0 at other providers
- 550 5.2.0External contact has no valid primary address.Exchange Online could not deliver to an external contact because its primary SMTP address is missing from its proxy addresses or invalid.
- 554 5.2.0Clutter folder missing in the recipient mailbox.Delivery to one Exchange Online mailbox fails because Clutter is turned on for it but its Clutter folder is missing.
All 105 standard codesEvery code in the wikiPaste your own bounce