Generic SMTP delivery response
Understand SMTP 5.2.1: Mailbox disabled
The destination mailbox exists but is disabled or otherwise configured not to accept messages.
A representative response is:
550 5.2.1 Mailbox disabled.
The 5.x response is permanent for this attempt. The recipient or mailbox administrator must restore acceptance before retrying.
What this response means
Standard 5.2.1 Mailbox disabled, not accepting messages means the recipient object exists but currently refuses mail. The reason can be suspension, deprovisioning, policy, billing, or an administrator action.
What to do
- Confirm that the recipient address is correct.
- Contact the recipient through another channel and ask whether the mailbox is still active.
- If you manage the mailbox, check license, suspension, login state, delivery restrictions, retention, and recent deprovisioning.
- Restore the mailbox or approved alias only if it should still receive mail.
- For automated sending, suppress the address until its owner confirms recovery.
Do not keep retrying a permanent 5.2.1 response and do not change sender DNS to reactivate someone else’s mailbox.
Who can fix it
The recipient or receiving-mail administrator controls mailbox status.
Related troubleshooting
Use a recipient-not-found guide if the later response says the mailbox no longer exists.
Frequently asked questions
What does SMTP 5.2.1: Mailbox disabled mean?
The mailbox exists but has been disabled or configured not to accept messages. Its owner or receiving-mail administrator controls the fix.
Can MailFixIt prove this entire bounce from public DNS?
No. The current checker can evaluate selected public DNS configuration, but it cannot recreate recipient state, credentials, reputation, message content, or a historical provider SMTP decision.
Related email diagnostics
Primary sources: IANA SMTP Enhanced Status Codes.