Microsoft weights sender reputation via SNDS and JMRP, and rejects unauthenticated bulk mail to consumer Outlook.com addresses.
What email bounce handling is#
Bounce handling is the automated processing of delivery failure notices (DSNs) to classify hard versus soft bounces and suppress addresses accordingly.
Why it matters#
Repeatedly sending to invalid addresses is one of the strongest negative reputation signals providers track.
Setting up email bounce handling for Outlook and Microsoft 365#
- 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 Outlook and Microsoft 365 reports results#
Open a delivered test message in Outlook and Microsoft 365 and view the original or headers. Look for Authentication-Results and any provider-specific verdict headers. Use the provider's sender dashboard for aggregate reputation.
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.
Does Outlook and Microsoft 365 require email bounce handling?
Microsoft weights sender reputation via SNDS and JMRP, and rejects unauthenticated bulk mail to consumer Outlook.com addresses. Treat email bounce handling as required for any meaningful volume.