Free email bounce analyzer
Why did this email bounce?
Paste a bounce message or SMTP error. Get the failure type, standardized status meaning, retry guidance, and the exact next checks — entirely in your browser.
Private by design: pasted text never leaves this browser.
How the analyzer reads a bounce
Delivery Status Notifications use structured fields defined by RFC 3464. The analyzer prefers the per-recipient Status field, then the SMTP reply preserved in Diagnostic-Code, and finally recognizable codes and phrases in human-readable bounce text.
Enhanced codes follow the class.subject.detail form defined by RFC 3463 and its registry. The first digit says success, temporary failure, or permanent failure. The remaining digits narrow the problem to an address, mailbox, mail system, routing, content, or security/policy category.
Provider prose still matters. A broad code such as 5.7.1 can cover several policy failures, so the result separates the standardized meaning from inferences based on words such as SPF, rate limit, reputation, relay, or message size. Low-confidence text is never presented as a certain diagnosis.
Common questions
Is it safe to paste a bounce message here?+
The parser runs entirely in your browser. The bounce text is not uploaded, logged, or placed in analytics. Analytics receives only categorical events such as temporary versus permanent failure, never domains, addresses, headers, or message text.
What is the difference between a 4.x.x and 5.x.x status?+
A 4.x.x enhanced status is a persistent temporary failure: a later attempt may work. A 5.x.x status is permanent for the message as sent, so something about the recipient, message, routing, authentication, or policy must change before it is retried.
Should I immediately retry a soft bounce?+
Usually no manual action is needed because a normal sending server queues the message and retries with backoff. Repeated immediate retries can worsen throttling. Investigate if the same temporary failure persists beyond your provider's queue window.
Why can the same 5.7.1 code mean different things?+
Enhanced codes provide a standardized category, but providers attach their own diagnostic text and policies. X.7.1 broadly means delivery was not authorized and the message was refused; the surrounding text might identify relay permissions, authentication, reputation, content, or another policy.
What parts of a DSN matter most?+
Start with Action, Status, and Diagnostic-Code. Status gives the standardized enhanced code. Diagnostic-Code preserves the SMTP reply and provider-specific explanation. The reporting server and recipient fields provide context but are not needed for this tool to classify the cause.
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