Email Bounce Code Decoder
Read what a bounce message actually says, and whether it will retry.
Common codes
- 4.2.2 — The recipient mailbox is full.
- 4.4.1 — No answer from the receiving server.
- 4.4.2 — The connection was dropped mid-delivery.
- 4.7.0 — Temporarily deferred by a policy — commonly greylisting or rate limiting.
- 4.7.1 — Delivery temporarily refused for policy reasons.
- 5.1.1 — The mailbox does not exist at that domain.
- 5.1.2 — The domain does not exist or has no mail servers.
- 5.1.8 — The sender address is invalid or its domain does not exist.
- 5.2.1 — The mailbox exists but is disabled.
- 5.2.2 — The mailbox is full, and the receiver treats that as permanent.
- 5.4.1 — No answer from the destination and the receiver has given up.
- 5.7.1 — Delivery refused by policy — relaying denied, blocked sender, or failed authentication.
- 5.7.13 — The sending account is not permitted to send as that address.
- 5.7.26 — The message failed authentication — no aligned SPF or DKIM.
- 5.7.509 — The receiver could not authenticate the sender and requires DMARC alignment.
How this lookup works
Paste the bounce and the enhanced status code is extracted and explained. The first digit is the part almost nobody reads and the part that decides what to do: 4 is temporary and the sending server retries automatically for days, while 5 is permanent and it will not. Treating a 4.x.x as a dead address removes subscribers who were never unreachable; treating a 5.x.x as temporary leaves a sending reputation burning while a queue retries an address that will never accept mail.
What the results mean
- 4.x.x
- Temporary. The sender retries automatically, usually over several days, and most resolve without anyone doing anything.
- 5.x.x
- Permanent. No retry. The address should not be sent to again until something changes.
- 5.1.1
- The mailbox does not exist. The single most common permanent bounce, and the one that damages sender reputation if repeated.
- 5.7.x
- Refused by policy — authentication, reputation or relaying. The family that points at your own configuration rather than the recipient.
- 4.7.0
- Frequently greylisting: a first message from an unknown sender is deliberately deferred and arrives on the retry.
Common problems and fixes
- Everything to one provider bounces at once
- That is reputation or authentication, not addresses. Check SPF, DKIM and DMARC alignment, then whether the sending IP is on a blocklist.
- The bounce says 4.7.1 repeatedly
- Sustained temporary policy rejections mean throttling based on reputation. More retries will not help; sending volume and authentication will.
- A valid address bounced as 5.1.1
- Check the domain for a typo first, then whether the mailbox was recently deleted. Some providers also return 5.1.1 for disabled accounts.
Frequently asked questions
What is the difference between a hard and a soft bounce?
A hard bounce is a 5.x.x code — a permanent failure that will not be retried, such as a mailbox that does not exist. A soft bounce is 4.x.x — temporary, retried automatically, and usually resolved by the retry. The distinction matters because removing addresses on soft bounces loses real subscribers, and keeping addresses that hard-bounce damages your reputation with every attempt.
What does 5.7.1 mean?
Delivery refused by policy. It is the catch-all for relaying denied, blocked sender, and failed authentication, which is why it is common and unhelpful on its own. Check SPF, DKIM and DMARC alignment first, then blocklists — the receiver rarely says which of them it meant.
Should I retry a bounced message?
For a 4.x.x, your mail server already is — sending again by hand adds load and nothing else. For a 5.x.x, no: the receiver has answered definitively, and repeated attempts to a permanently failing address are exactly what reputation systems are watching for.
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