550 SMTP bounce: mailbox unavailable
What 550 means
The receiver refused the recipient or the message for a permanent reason: the mailbox does not exist, or a policy rejected it. Do not retry unchanged.
Message text
Requested action not taken: mailbox unavailable (e.g., mailbox not found, no access, or command rejected for policy reasons)
Common causes of 550
- Recipient address has a typo or the mailbox does not exist
- Receiving policy (SPF, DKIM, DMARC, reputation or content) rejected the message
- Recipient mailbox was removed or disabled
How to fix 550
- Re-check the recipient address for typos.
- If the address is correct, check authentication with SPF checker, DKIM checker and DMARC checker.
- Check your sending IP with blocklist check.
- Read the enhanced code (5.x.x) in the bounce; it narrows the cause.
Check your domain
Check the SPF record of your sending domainRuns in your browser; nothing is uploaded.
Have the full bounce message? Paste it into the bounce code lookup and it will match the code and the provider for you. Open the bounce code lookup.
How to read 550
The first part, 550, is the SMTP reply code. Requested action not taken, mailbox unavailable: the mailbox does not exist, is not allowed, or the message was refused for policy reasons. Replies that start with 4 are temporary and replies that start with 5 are permanent (RFC 5321 §4.2.1).
This reply carries no enhanced status code. The three-digit reply code is the only machine-readable signal, so read the text that follows it to learn the reason.
Do not keep resending the same message: a permanent failure repeats until the cause is fixed. Correct the cause, then send a new message.
Official source: www.rfc-editor.org. Last verified 2026-10-20.
Related guides
- How to create an SPF record (syntax and examples)
- How DKIM works and how to publish a DKIM record
- How to set up a DMARC record, from p=none to p=reject
Related codes
- 551 SMTP: user not local
- 552 SMTP: storage exceeded
- 553 SMTP: mailbox name not allowed
- 554 SMTP: transaction failed
- 5.1.1 SMTP: bad destination mailbox
- 5.1.2 SMTP: bad destination system
FAQ
What does 550 mean?
The receiver refused the recipient or the message for a permanent reason: the mailbox does not exist, or a policy rejected it. Do not retry unchanged. This is a permanent failure.
How do I fix 550?
Re-check the recipient address for typos. If the address is correct, check authentication with SPF checker, DKIM checker and DMARC checker. Check your sending IP with blocklist check. Read the enhanced code (5.x.x) in the bounce; it narrows the cause.
Is 550 permanent, and should I retry?
550 is a permanent failure, so retrying the same message will fail again. Fix the cause first, then send a new message.