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SMTP error code · Standard (RFC)

SMTP 550: requested action not taken, mailbox unavailable

550 Permanent failure (5xx): the message bounced
By iBlockSpam Team Checked against sources 3 sources How we check our content
What it means

The receiving server permanently refused the message for this recipient: the mailbox doesn't exist, you don't have access, or a policy rejected it.

What the bounce says
550 5.1.1 The email account that you tried to reach does not exist.

Start of Gmail's text for a non-existent address, one of many 550 replies.

What 550 means

RFC 5321 defines 550 as "Requested action not taken: mailbox unavailable (e.g., mailbox not found, no access, or command rejected for policy reasons)". That's a wide range, which is why 550 is the code you'll see most in bounces. It is permanent: your server stops trying and sends you a bounce.

The enhanced status code that follows the 550 tells you which kind of 550 you have. The middle number is the key. X.1.x is about the address, so 5.1.1 means the mailbox doesn't exist. X.2.x is about the mailbox. X.7.x is security or policy: 5.7.1 is a general policy refusal, 5.7.23 is an SPF failure, 5.7.25 is a reverse DNS failure, and 5.7.26 means several authentication checks failed.

Provider codes go further. Microsoft 365 uses codes such as 5.7.509 for DMARC rejections and 5.7.606 to 5.7.649 for blocked IP addresses. Gmail adds text explaining the reason and a link to its help pages. Search the full code in the lookup above to get the specific meaning.

Likely causes

  • The recipient address doesn't exist or was mistyped (usually 5.1.1).
  • The receiver's policy rejected the message or the sender (usually 5.7.x).
  • Your domain's SPF, DKIM or DMARC checks failed.
  • Your sending IP address is on a blocklist or has a poor reputation.

How to fix it

If you sent the message

  1. Read the enhanced code and text after the 550, then look it up for the specific cause.
  2. For address errors, check the spelling and confirm the address with the recipient.
  3. For 5.7.x policy errors, check your SPF, DKIM and DMARC records and your IP's blocklist status.

If you're the recipient or their admin

  1. If senders tell you mail to an existing address bounces with 550, check the mailbox exists, is licensed and that your MX records point to the right service.
  2. Check your allow/block lists and mail flow rules for an entry that matches the sender.
Email Health Check Blacklist Checker DMARC Checker

Frequently asked questions

Does a 550 error mean I'm blocked?

Not necessarily. A 550 can mean the address doesn't exist, that you lack permission to send to it, or that a policy rejected the message. The enhanced code after it (5.1.1, 5.7.1 and so on) tells you which.

Should I resend a message that bounced with 550?

Only after you fix the cause. RFC 5321 says the client should not repeat the exact request after a permanent error. Correct the address or your setup first, then resend.

What is the difference between 550 and 554?

Both are permanent. 550 is about a mailbox (not found, no access or a policy refusal for that recipient). 554 means the transaction failed, and is often used for refusals that apply to the whole message or connection.

Sources

  1. RFC 5321: Simple Mail Transfer Protocol (reply codes, section 4.2)
  2. RFC 3463: Enhanced Mail System Status Codes
  3. Email nondelivery reports (NDRs) and SMTP errors in Exchange Online (Microsoft Learn)

Provider messages are quoted as the provider publishes them. Servers can change their wording, so the bounce you received may differ slightly.

Related codes

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