Compile your findings
Gather all checked items, error messages, and key findings into a summary.
Identify exposure in 30 minutes
Exchange Online diagnostic checklist: Prevent audit findings and outages
Complete this 40+ item checklist to identify configuration gaps, security misconfigurations, and hidden threats before they trigger audit findings or user impact. Covers mail flow, Outlook connectivity, hybrid coexistence, access control, and threat indicators. Download as PDF for offline incident use. After completing: Schedule a security assessment to get remediation plan and compliance validation.
1. General information
Collect this before any troubleshooting step.
2. Mail flow issues
Use this checklist if mail is not flowing or being received.
Mail flow pre-checks
Inbound mail
Outbound mail
3. Outlook client issues
Use this checklist for authentication, connection, or stability problems.
Outlook pre-checks
Authentication & sign-in
Autodiscover & connectivity
Outlook profiles
4. Hybrid & mailbox move issues
Use this checklist for namespace, HCW, or migration problems.
Hybrid pre-checks
Namespace & DNS
Mailbox moves
5. Security & compliance checks
Use this checklist for security events, policy violations, or compliance audits.
6. Performance & quota issues
Use this checklist for slow performance, quota limits, or throttling.
Next steps
Once you've completed your diagnostic, share with principal engineers for expert guidance.
Submit to ExchangeGuardians
Contact us with your tenant domain, impact scope, error codes, and timeline.
Get a principal response
We'll provide a root-cause analysis, production-safe fix steps, and rollback plan within 2 hours.