Repeatedly sending to invalid addresses is one of the strongest negative reputation signals providers track.
How to implement email bounce handling#
- 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.
How to verify it worked#
Send a test message to seed mailboxes at Gmail, Outlook, and Yahoo, then inspect the Authentication-Results and delivery headers. Repeat after any DNS or sending-platform change.
Common mistakes#
- Treating 'mailbox full' as a hard bounce and losing valid contacts.
- Ignoring 'blocked by policy' bounces that signal a blocklist or DMARC failure.
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.