A bounce is a delivery-status notification generated when a message cannot be delivered. It may describe a permanent problem with the address or domain, or a temporary condition such as throttling, a full mailbox or an unavailable destination server.
Bounces should be recorded with the original recipient, time, SMTP response and enhanced status code. That evidence makes it possible to separate list-quality problems from temporary provider or infrastructure issues.
Permanent failures
A permanent failure is normally represented by a 5xx SMTP response. Non-existent recipients, invalid domains and addresses that have been disabled should be suppressed rather than repeatedly retried.
Continuing to send new messages to known invalid recipients wastes capacity and signals poor list management to mailbox providers.
Temporary failures
A 4xx response usually indicates a temporary deferral. The message should remain queued and be retried with controlled backoff. Repeated temporary failures should still be reviewed: a mailbox that remains full or unavailable over several campaigns may no longer be useful.
- Keep the original SMTP response for diagnosis.
- Do not treat provider throttling as an invitation to retry aggressively.
- Separate a transport retry from sending a fresh campaign copy.
- Set a sensible queue lifetime for genuinely temporary conditions.
Watch the trend, not just one number
A sudden rise in failures can indicate an old list, a broken import, a compromised form, DNS trouble or a reputation problem at a particular provider. Compare results by campaign, source, recipient domain and failure class.
AuthSMTP customers can review recent account errors in the Control Panel. If a pattern is unclear, preserve the complete response and include it when contacting support.
Suppress permanent failures promptly, retry temporary failures carefully and investigate any sustained increase in bounce rates.
Confirm that your application records bounce responses, immediately suppresses clear permanent failures and limits retries for persistent temporary failures.