Hard vs soft bounce triage

Is this a permanent rejection you must suppress — or a transient hiccup worth retrying?

Paste the bounce response — the body of a mailer-daemon message, the Delivery Status Notification report, the SMTP transcript — and we'll run a deterministic classifier over the RFC 3463 DSN classes (`4.x.x` / `5.x.x`) and the SMTP status codes (`4xx` / `5xx`), then ask the analyst for a hard / soft / mixed / unknown verdict, a 0-100 bounce-rate score, the strongest 3-5 signals driving it, and a short list of plain-English remediation tips.

Paste the bounce or SMTP response — get a hard / soft classification
Paste the body of a mailer-daemon message, the Delivery Status Notification report, or the SMTP transcript (anything containing `Diagnostic information`, `RCPT TO`, `550 5.1.1`, or a DSN class). The checker extracts the DSN classes and the SMTP status codes, sends a compact envelope to the analyst, and returns a hard / soft / mixed / unknown verdict plus a 0-100 bounce-rate score.
See bounce rate trends over time?
One email and we'll let you know when ReputaPilot opens up — continuous bounce tracking per ESP, per sending domain, per recipient subdomain, with an alert the moment a hard-bounce class appears in your DSN stream.

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FAQ

Bounce rate checker — frequently asked questions

Pair this checker with the guide

Want the explanation behind every code the checker surfaces?

The SMTP bounce codes pillar explains every DSN class and every SMTP status the checker flags — what `5.1.1 user unknown` means, what `4.2.2 mailbox full` is trying to tell you, when `4.7.1` is greylist versus blocklist, how `5.7.606` from Microsoft differs from `5.7.1` spam content rejected. Pair the verdict this checker returns with the long-form explanation so every suppression decision lands on a specific code, not a vague "delivery failed". If hard bounces point to a reputation issue, run the blacklist lookup checker to check the sending domain or IP.

Read the SMTP bounce codes guide →