Setup checklist#
- ☐ Parse DSN codes: 5.1.x means the address does not exist (hard); 4.x.x means temporary (soft).
- ☐ Suppress hard bounces after one failure and soft bounces after three.
- ☐ Route bounce notifications to a monitored mailbox or webhook.
- ☐ Review bounce reasons weekly for patterns like 'blocked' that indicate reputation issues.
Audit checklist#
- ☐ Confirm you are not: treating 'mailbox full' as a hard bounce and losing valid contacts.
- ☐ Confirm you are not: ignoring 'blocked by policy' bounces that signal a blocklist or DMARC failure.
Ongoing monitoring#
- ☐ Weekly: review provider dashboards (Postmaster Tools, SNDS) and bounce logs
- ☐ Monthly: re-run the setup verification after any vendor or DNS change
- ☐ Quarterly: full audit against this checklist
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.