What it looks like in your logs
550 5.1.1 <user@example.com>: The email account that you tried to reach does not exist. Please check the address for typos. - mx.example.comWhat does 550 mean?
RFC 5321 defines 550 as a requested action not taken because the mailbox is unavailable, for example not found or no access. It is the most common permanent failure in email and your server will not retry it. If you send to the same address again, you will get the same answer and your reputation takes another small hit. That makes every 550 worth handling promptly.
The three digits alone do not tell you whether the problem is the address or you. A 550 5.1.1 means the mailbox does not exist, and the fix is to suppress it. A 550 5.7.1 or 550 5.7.26 means the receiver refused the message on policy or authentication grounds, and the address may be perfectly valid. Always read the enhanced code before deciding what to do.
Gmail returns 550 5.1.1 for unknown users, 550 5.7.1 for messages it considers unsolicited, and 550 5.7.26 for DMARC failures. Microsoft 365 uses 550 5.1.1 for invalid recipients and a range of 550 5.7.x codes for blocked senders. Yahoo uses 550 and 554 with bracketed tags for address and policy rejections.
Soft or hard bounce?
| Soft bounce (4xx) | Hard bounce (5xx) | |
|---|---|---|
| Nature | Temporary | Permanent |
| Sender behaviour | Queue and retry with backoff | Stop, suppress the address |
| Reputation risk | Low, unless it repeats for days | High above a 2% bounce rate |
| 550 | ✓ this code |
Common causes
- The recipient address does not exist, often because of a typo or a deleted account.
- The mailbox was disabled or the employee left the organization.
- Your sending IP or domain is on a blocklist the receiver uses.
- The message failed SPF, DKIM or DMARC and the receiver enforced a reject policy.
- Content or reputation filters classified the message as spam.
- The recipient organization explicitly blocks your domain or address.
How to fix 550
- Read the enhanced code: 5.1.x means an address problem, 5.7.x means a policy, reputation or authentication problem. See 5.1.1 and 5.7.1 for each path.
- For address failures, suppress the address immediately and never retry it.
- For policy failures, check your IP with the blacklist checker and your records with the SPF checker and DMARC checker.
- Run the rest of the list through an email verifier (ZeroBounce, NeverBounce or SendPulse's email verifier) before the next campaign, so similar bad addresses are caught first.
- Add double opt-in to signup forms so typos never reach your list.
- Keep your hard bounce rate well under 2%; the bounce rate guide explains how to measure it.
550 questions
What does SMTP error 550 mean?
It means the receiving server permanently refused your message. Usually the mailbox does not exist, but 550 is also used when your IP, domain, authentication or content fails a policy check. The enhanced code after 550, such as 5.1.1 or 5.7.1, tells you which one applies.
Is SMTP 550 a hard bounce?
Yes. Any 5xx reply is a permanent failure, and 550 is the most common hard bounce. When the enhanced code is 5.1.x, suppress the address. When it is 5.7.x, the address may be fine and the block is about you, so fix the underlying cause before sending again.
How do I fix a 550 error in Gmail or Outlook?
Look at the full bounce text. If it says the account does not exist, remove the address. If it mentions policy, spam, SPF or DMARC, check your authentication with the DMARC checker and your IP with the blacklist checker. Our header analyzer can also show how a test message was authenticated.
Can a 550 error mean my IP is blacklisted?
Yes. Many providers return 550 5.7.1 or a similar code when your sending IP is on their own blocklist or a public one such as Spamhaus. The bounce text usually names the list. Check with the blacklist checker and follow our blacklist removal guide to request delisting after fixing the cause.