Microsoft is looking into a newly identified issue in classic Outlook that prevents users from opening certain encrypted emails following a recent software update.
The bug affects users who updated to the Current Channel Version 2511 (Build 19426.20218). According to Microsoft, recipients are unable to open emails with the “Encrypt Only” setting. While this option encrypts messages, it still allows actions like copying, printing, and forwarding — making it popular for routine secure communication.
However, impacted users report seeing a warning in the Reading Pane stating that the message cannot be viewed until credentials are verified. When users attempt to open the email fully, the message content is replaced by an attachment named message_v2.rpmsg, making the actual message unreadable.
Microsoft confirmed the issue in an advisory, stating that the Outlook team is actively investigating a fix, though no estimated timeline has been announced for when a permanent solution will be released.
Temporary Workarounds Available
Until a permanent solution is released, Microsoft has suggested a few temporary workarounds. One option is for senders to encrypt emails using the Options tab in Outlook instead of encrypting messages through the File > Encrypt menu. By choosing “Encrypt” or “Do Not Forward” from the Options tab, recipients are able to open the messages normally.
Alternatively, affected users can roll back Outlook to an earlier version that does not include the bug. Microsoft noted that Build 19426.20186 does not exhibit the problem. To roll back, users must close all Office applications and run a specific command via an elevated Command Prompt.
Ongoing Outlook Reliability Issues
This incident is the latest in a series of issues impacting classic Outlook users. In November, Microsoft mitigated an Exchange Online outage that blocked access to mailboxes via classic Outlook. A month earlier, it fixed a bug that prevented Microsoft 365 users from opening Outlook on Windows systems.
Microsoft has also fixed performance issues causing CPU spikes while typing emails and disruption in drag-and-drop functionality after Windows 24H2 updates. Additionally, the company has previously issued temporary fixes for encryption-related errors and crashes triggered when opening or composing emails.
For now, users who depend on encrypted emails in classic Outlook are advised to follow the recommended workarounds while Microsoft works toward a permanent fix.
