Fix OME Encrypted Emails Not Opening for External Recipients
Question details
External recipients are unable to open Microsoft 365 OME encrypted emails, requiring an adjustment to the Outlook Web App policy MIME settings.
- Product
- Exchange Online
- Device & OS
- not provided
- Scenario
- An administrator needs to restore access for external recipients who are receiving Microsoft 365 OME encrypted emails but cannot successfully open them.
- Observed behavior
- When external users receive an OME encrypted email, the email wrapper or content fails to load or open properly due to restricted MIME type settings on the Exchange server.
Ensure you have Exchange Online administrator privileges and access to the Exchange Online PowerShell module before attempting to modify mailbox policies.
Reset MIME Settings using Exchange Online PowerShell
Use PowerShell to update the default Outlook Web App policy, specifically modifying how 'text/html' MIME types are handled for encrypted messages.
This solution requires connecting to your Microsoft 365 environment via PowerShell to adjust the OwaMailboxPolicy. By forcing the save of the 'text/html' MIME type, the encrypted message wrapper can render properly for external recipients.
Open PowerShell on your computer as an administrator and connect to Exchange Online using the command: Connect-ExchangeOnline.
Run the command `$owapolicy = Get-OwaMailboxPolicy` to fetch the identity and current configuration of your Outlook Web App mailbox policy.
Execute the command `Set-OwaMailboxPolicy -AllowedMimeTypes @{remove = "text/html"} -BlockedMimeTypes @{remove = "text/html"} -ForceSaveMimeTypes @{add = "text/html"} -Identity $owapolicy.Identity` to reset the handling of HTML content.
Allow up to 30 minutes for the policy changes to fully propagate across the Microsoft 365 servers.
Manage and Protect Your Documents with WPS Office
While Exchange Online manages your encrypted email routing, handling the actual documents and attachments securely is just as important. WPS Office is a highly compatible, free, and lightweight alternative to Microsoft Office that lets you view, edit, and protect your files with ease.
- 1. Download the Installer: Visit the official WPS website and download the free installation package for your operating system.
- 2. Install WPS Office: Run the setup file and follow the on-screen prompts to complete the installation.
- 3. Secure Your Documents: Open your Microsoft Office formats in WPS and navigate to the security tab to apply custom document encryption.
Frequently Asked Questions
Why can't external users open my OME encrypted emails?
This generally happens when the Exchange Online Outlook Web App (OWA) policy restricts the 'text/html' MIME type, preventing the encrypted email's HTML wrapper from rendering correctly for users outside your organization.
How long does it take for the OWA policy changes to apply?
It typically takes up to 30 minutes for MIME policy changes made via Exchange Online PowerShell to fully synchronize and propagate across all Microsoft 365 servers.
Do I need special permissions to fix this OME issue?
Yes, you must have Exchange Online administrator credentials to connect to the Exchange Online PowerShell module and modify the organizational OWA mailbox policies. If you are not an administrator, you must request assistance from your IT department.
What should I do if the PowerShell fix doesn't work?
If more than 30 minutes have passed and encrypted emails are still unreadable, log into the Microsoft 365 admin center and navigate to Support > Service requests to escalate the issue to the Microsoft engineering team.
