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Permanent failure — do not retry
BlockAbout your sending, not the address

SMTP 550 5.7.1

message refused by policy

SMTP 550 5.7.1 means the recipient's server recognised the address but refused the message on policy grounds — failed authentication, a blocklisted sending IP, or content its filters rejected. Unlike 5.1.1, the mailbox is fine; the problem is you, or your sending infrastructure.

Should you remove the address?

Keep the address; fix the sending side

Usually keep it. The block is about your sending or the recipient's policy, not proof the address is dead. The exception is a restricted group that will never accept outside mail; drop that from cold lists.

Block. Retrying changes nothing until the cause on your side is fixed.

How it appears

550 5.7.1 Unauthenticated email from example.com is not accepted due to domain's DMARC policy.

550 5.7.1 Service unavailable; Client host [203.0.113.5] blocked using Spamhaus

550 5.7.1 Message rejected due to content restrictions

What causes it

  • SPF, DKIM or DMARC failed, and the recipient domain publishes p=reject.
  • Your sending IP or domain appears on a blocklist the recipient consults.
  • The recipient server requires authentication you did not provide, or refuses relaying.
  • Content filtering rejected the message outright rather than filing it as spam.

How to fix it

In order — try the first one first.

  1. Check your SPF, DKIM and DMARC records first — a policy rejection usually means an alignment failure. Run a full audit on your sending domain.
  2. Check whether your sending IP is on a major blocklist. A listing explains a sudden, total delivery failure that otherwise looks inexplicable.
  3. Read the text after the code. Most servers name the specific reason, and many include a URL explaining their policy.
  4. If it started suddenly with no infrastructure change, look for a bounce or complaint spike that triggered the listing.

Who sends it

Everyone. Gmail uses it for spam and reputation blocks and malformed headers; Microsoft 365 uses it for restricted groups, relay denials and unauthenticated clients.

Common questions

What does SMTP 550 5.7.1 mean?
SMTP 550 5.7.1 means the recipient's server recognised the address but refused the message on policy grounds — failed authentication, a blocklisted sending IP, or content its filters rejected. Unlike 5.1.1, the mailbox is fine; the problem is you, or your sending infrastructure.
Should I retry a 550 5.7.1 error?
No. 550 is a permanent failure, so the message will never be delivered no matter how many times you try. Remove the address — repeated sends to permanent failures are one of the main signals mailbox providers use to throttle a sender.
How do I fix SMTP 550 5.7.1?
Check your SPF, DKIM and DMARC records first — a policy rejection usually means an alignment failure. Run a full audit on your sending domain.
Is 550 5.7.1 a hard bounce or a soft bounce?
550 5.7.1 is a block rather than a classic hard or soft bounce. The rejection is about your sending (authentication, reputation, content or the recipient's policy), not about whether the address exists. Retrying changes nothing until the cause on your side is fixed.
Should I remove the address after a 550 5.7.1 bounce?
Usually keep it. The block is about your sending or the recipient's policy, not proof the address is dead. The exception is a restricted group that will never accept outside mail; drop that from cold lists.
Will verifying my list prevent 550 5.7.1?
Not directly. This code is about your authentication, IP or domain reputation, so verification will not lift it. A clean list still matters, because mailbox providers weigh how often a sender hits addresses that don't exist.

Clean the list before the next send.

A bounce report only tells you about the addresses you already mailed. The rest of the list has the same kinds of dead mailboxes in it, and each one becomes a hard bounce recorded against your domain the moment you send.

  • A real SMTP mailbox check on every row, before anything is sent
  • Dead and mistyped addresses split out, so they never reach your sending tool
  • Catch-all, disposable and role addresses flagged alongside
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Other 550 replies

Sources

Provider wording is quoted only where the provider publishes it.

Last reviewed 2026-10-22

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