Bounce code lookup
Paste a bounced email, or just the error code. See what it means in plain words, whether it is a hard or soft bounce, and whose move it is: yours or the recipient's. Free, no signup, and the text stays in your browser.
How to read a bounce code
A bounce message has up to three parts, for example 550 5.1.1 The email account that you tried to reach does not exist:
- The reply code (550). Three digits. A code that starts with 4 is temporary; one that starts with 5 is permanent.
- The enhanced code (5.1.1). Three numbers with dots. The middle number is the subject: 1 is the address, 2 is the mailbox, 4 is the network, 7 is security and policy.
- The words. Each mail provider writes its own. They often say more than the numbers, which is why this tool reads the whole message and not only the code.
Hard bounce or soft bounce?
- hard A 5xx code. The mail server refused the message for good. Sending the same message again will fail again.
- soft A 4xx code. A temporary problem: the mail server is busy, the mailbox is full, or you are being slowed down. Mail servers retry these on their own, usually for a few days.
A hard bounce does not always mean a bad address. 550 5.1.1 is a bad address; 550 5.7.26 is a good address that refused your email because it failed authentication. Deleting the address fixes the first and does nothing for the second.
The codes people look up most
| Code | Seen at | Meaning | Whose move |
|---|---|---|---|
550 5.1.1 | Gmail, Microsoft 365, most servers | The mailbox does not exist. | Fix your list |
550 5.4.1 | Microsoft 365 | "Recipient address rejected: Access denied". The address does not exist. | Fix your list |
550 5.1.10 | Microsoft 365 | Recipient not found. | Fix your list |
553 5.1.2 | Gmail | The domain after the @ was not found. | Fix your list |
550 5.2.1 | Gmail | The account is inactive or disabled. | Fix your list |
552 5.2.2 | Gmail, most servers | The mailbox is full. | Wait and try again |
550 5.2.2 | Microsoft 365 | "Submission quota exceeded". Here it is the sender who sent too much, not a full mailbox. | Wait and try again |
421 4.7.0 | Gmail | Gmail does not trust the sending IP or domain yet and is slowing your mail down. | Fix your sending setup |
421 4.7.28 | Gmail | You sent too much, too fast. | Fix your sending setup |
550 5.7.1 | Gmail, most servers | Refused by policy: a spam filter, a block list or a rule set by the recipient. | Depends on the words |
550 5.7.26 | Gmail | SPF and DKIM did not pass, or the message failed DMARC. | Fix your sending setup |
550 5.7.509 | Microsoft 365 | The message failed DMARC and your domain's policy is "reject". | Fix your sending setup |
550 5.7.23 | Microsoft 365 | SPF failed for the domain you send from. | Fix your sending setup |
550 5.7.25 | Gmail, Microsoft 365 | The sending IP has no reverse DNS (PTR record). | Fix your sending setup |
550 5.7.511 | Microsoft 365 | Microsoft banned the IP address you send from. | Fix your sending setup |
550 5.7.133 | Microsoft 365 | The group only accepts mail from inside its own organisation. | Only the recipient side can fix it |
552 5.3.4 | Gmail | The message is over the size limit. | Change the message |
550 5.4.5 | Gmail | Your account reached its daily sending limit. | Wait and try again |
The lookup knows more codes than this table: the lists published by Google and Microsoft, and the standard codes in the IANA registry.
Each of the main codes has its own page with causes and fixes: see all bounce codes explained.
Which bounces a clean list fixes
Only the ones marked Fix your list: mailboxes that don't exist, domains that can't receive email, and disabled accounts. Remove those addresses, because every repeat bounce counts against your sender reputation.
Before you send, the email list checker finds the addresses with mistyped or dead domains. It does not log in to mail servers, so it cannot tell you whether a mailbox exists at a working domain; a bounce like 550 5.1.1 is how you find that out.
Bounces marked Fix your sending setup are about you, not the address. Start with the SPF, DMARC and DKIM checker for your own domain.
Questions
Where do I find the bounce code?
In the email that came back from "Mail Delivery Subsystem" or "Postmaster". Look for a line with a number like 550 5.1.1, often after "Remote server returned" or "Diagnostic-Code". If you send with an email service, the code is in its bounce or activity report.
Is my bounce message sent anywhere?
No. The text is read by a script in your browser. Nothing you paste is uploaded or stored.
The same code means different things at Gmail and Microsoft?
Sometimes. 5.2.2 is "mailbox full" at Gmail and "submission quota exceeded" (a sender limit) at Microsoft 365. That is why the tool looks at who sent the bounce and at the words, not only the number.
What if the code is not in the list?
The tool falls back to the general meaning of the code and to the words in the message, and says so. Small mail servers and spam filters often write their own text with a general code like 550 or 554.
Should I remove every address that bounces?
Remove hard bounces where the address or domain is the problem. Keep addresses that bounced because of a full mailbox, a busy server, or a block on your own sending: those addresses still exist.
More free checks
- Email list checker: check a whole list before you send.
- Email typo checker: find gmial.com and other mistyped domains.
- MX record checker: can a domain receive email at all?
- SPF, DMARC and DKIM checker: will Gmail and Outlook trust your emails?