Troubleshooting · Email
Email delivery failure
Outbound mail is rejected or quarantined, or expected inbound mail never arrives.
Work through these in order
- 01
Read the bounce message
The enhanced status code and remote server response usually name the exact cause.
- 02
Check domain authentication
SPF includes the sending source, DKIM signs and aligns, DMARC policy is satisfied.
- 03
Check reputation and listings
Sending IP or domain on a blocklist, often after a compromised account sent bulk mail.
- 04
Check transport rules and connectors
A single rule can silently redirect, block or reroute large volumes of mail.
- 05
Trace the message
Use message trace to determine whether it left, was filtered, quarantined or delivered to a rule created folder.
- 06
Check for compromise indicators
New inbox rules or external forwarding on the affected mailbox.
Background reading
Email Security
Protecting the most used attack channel with authentication, filtering, link and attachment analysis, and user reporting.
Exchange Online
Microsoft's cloud email service, including transport rules, connectors, mailbox permissions and hybrid coexistence with on premises Exchange.
DNS
The Domain Name System is the distributed, hierarchical directory that resolves names to addresses and service records for nearly every other service.