Bounce handling is the automated processing of delivery failure notices (DSNs) to classify hard versus soft bounces and suppress addresses accordingly.
What good looks like#
- Done: Parse DSN codes: 5.1.x means the address does not exist (hard); 4.x.x means temporary (soft).
- Done: Suppress hard bounces after one failure and soft bounces after three.
- Done: Route bounce notifications to a monitored mailbox or webhook.
- Done: Review bounce reasons weekly for patterns like 'blocked' that indicate reputation issues.
What bad looks like#
- Seen in audits: Treating 'mailbox full' as a hard bounce and losing valid contacts.
- Seen in audits: Ignoring 'blocked by policy' bounces that signal a blocklist or DMARC failure.
How to move from bad to good#
Work through the good list in order and re-verify after each change. Most teams find one or two items from the bad list already present; fixing those usually produces the largest improvement.
Frequently asked questions#
What is the difference between a hard and soft bounce?
Hard bounces are permanent failures (bad address). Soft bounces are temporary (full mailbox, server down). Suppress hard immediately.