5.2.1: mailbox 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.
- Standard
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 5.2.1
- 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
5.2.1 Mailbox disabled, not accepting messages
What it means
RFC 3463 describes X.2.1 as a mailbox that exists but does not accept messages, and says the error may be permanent if the mailbox will never be re-enabled, or temporary if it is only disabled for a while. So 5.2.1 means the message was returned, and 4.2.1 means the sending server will retry. Providers use it for accounts that were suspended, deactivated after a long period without use, or blocked by an administrator. A mailbox that stays disabled behaves like an unknown address, and should be treated as a hard bounce once the code repeats.
Common causes
- An account suspended by its provider or administrator.
- A mailbox deactivated after a long period without sign-ins.
- An account in the middle of being closed or migrated.
How to fix it
- 01For 4.2.1, let the retries run; the account may be re-enabled.
- 02If 5.2.1 repeats over several sends, remove the address or mark it as bounced.
- 03Contact the recipient another way and ask whether they have a new address.
- 04Recipient admins: re-enable the mailbox, or set up forwarding if the person has moved.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
Related codes
- 5.2.0Mailbox problem, unspecified.The recipient's mailbox exists, but something about it stopped the delivery and the receiving server did not say what.
- 5.1.6Mailbox has moved.The address used to be valid, but the mailbox no longer takes mail and the server has no new address to forward the message to.
- 5.1.1Mailbox does not exist.The recipient's domain accepts mail, but the mailbox named before the @ does not exist there, so the message was refused and will not be delivered.
- 550Mailbox unavailable.The receiving server permanently refused the message for this recipient: the mailbox does not exist, cannot be reached, or the server rejected the message by policy.
5.2.1 at other providers
- 550 5.2.1Recipient account is inactive.The Gmail account you wrote to is disabled or inactive, so it cannot receive mail, and Gmail rejected your message permanently.
- 550 5.2.1Recipient receiving too much mail.Gmail permanently rejected your message because the recipient's account is receiving mail faster than Gmail lets it accept.
Further reading
All 105 standard codesEvery code in the wikiPaste your own bounce