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1.13. Handling Encrypted Outlook Messages

Updated: Jun 10 2026, 04:25 PM

Encrypted (protected) Outlook messages can fail to display correctly when the mailbox that receives the message is not accessible in the standard Outlook web portal experience. This is commonly seen when attempting to view protected messages in a shared or routed mailbox workflow.

Cause

The message store for encrypted messages is not external to the mailbox. This can prevent recipients from opening protected messages (or viewing embedded images) when clicking links such as Read the message, because the content is tied to the mailbox where it was delivered.

Resolution - Decrypt messages using an Exchange mail flow rule

Create a server-side mail flow rule in the Exchange Admin Center to decrypt protected messages for the affected recipient address.

Steps

1. Open the Exchange Admin Center.
2. Go to Mail flow.
3. Add a new rule.
4. Configure the rule so messages for the affected address are decrypted on the server side.
5. Save the rule.

Example rule