How to Fix Outlook Revoked Security Certificate Warning for Microsoft 365
Question details
The user is encountering a security error in Outlook stating that the certificate for outlook.office365.com has been revoked.
- Product
- Microsoft Outlook
- Device & OS
- not provided
- Scenario
- Attempting to connect to Microsoft 365 services via the Outlook desktop application.
- Observed behavior
- Outlook displays a warning that the connection should not be trusted because the Microsoft 365 security certificate (from a trusted authority like DigiCert) has been revoked.
Do not bypass the security warning or attempt to manually install the revoked certificate, as this could expose your email communications to security risks.
Verify and Correct System Date and Time
Incorrect system clock settings are a primary cause of false certificate validation failures.
Security certificates have strict validity periods. If your computer's date and time are out of sync with real time, Outlook may mistakenly believe the current Microsoft 365 certificate is invalid or revoked.
Right-click on the clock displayed in the bottom-right corner of your Windows taskbar and select 'Adjust date/time'.
Ensure the toggle for 'Set time automatically' is turned on.
Click the 'Sync now' button to force Windows to update its time from the internet time server. Once synced, restart Outlook.
Temporarily Disable Antivirus Network Inspection or Proxies
Third-party security software or network proxies intercepting traffic can replace certificates and trigger the warning.
Install the Latest Windows and Outlook Updates
Outdated operating systems may lack the latest root certificates required to establish a trusted connection.
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Frequently Asked Questions
Why does Outlook say the security certificate is revoked?
This warning typically occurs when your system clock is out of sync, an antivirus program is intercepting encrypted web traffic, or your local root certificate cache is outdated.
Is it safe to install the revoked certificate to bypass the warning?
No. Manually installing a revoked certificate bypasses essential security checks and could leave your email communications vulnerable to interception or man-in-the-middle attacks.
How do I fix the outlook.office365.com certificate error on a corporate network?
If you are on a corporate network, the issue might be caused by your organization's firewall or proxy settings. Contact your IT administrator so they can configure the network to properly trust Microsoft 365 endpoints.
