Information Rights Management Issue when opening encrypted emails

this seems to fix it or at least work around it

HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\DRM 

Name: PreferredRmsPackage 

Type: DWORD 

Value: 1 

Dear @Jadyn Maxwell, 

I hope you're having a nice day. Thank you for reaching out to the Microsoft Q&A forum and for sharing the details of your issue. 

I understand how disruptive it can be when IRM-protected emails fail to open in Classic Outlook, even though they work correctly in New Outlook and Outlook on the Web. 

This issue is likely related to how Classic Outlook handles IRM authentication, where the service may fail to initialize properly, resulting in credential loops or unreadable protected content, unlike in newer Outlook versions. To help narrow this down further, could you confirm the following: 

1. Are you the IT administrator in your organization? 
2. Is this issue affecting your colleagues as well, or is it only happening to you?  
3. Are you using a personal device or one that is managed by your organization? 
4. Have you tested this behavior on a different device or user profile to rule out local configuration issues? 
5. Is the affected account part of an Azure Active Directory tenant with Conditional Access policies or MFA enabled?  
6. Are you using the latest version of Classic Outlook with all updates applied? 

This will help us better understand the context and provide more targeted support. Any additional information will help us better understand and support you.     

While we gather that information, here are some steps you can try in the meantime to help identify the issue:  

1/ Basic Checks 

• To begin, please ensure that Classic Outlook is fully updated to the latest version. This helps eliminate compatibility issues that may affect IRM functionality. 
• Next, try signing out of your Microsoft 365 account in Outlook and signing back in. This refreshes your credentials and may resolve authentication-related errors. 
• You should also check your device’s connectivity to IRM-related endpoints. I recommend running the Microsoft 365 Network Connectivity Test to verify access to essential domains such as *.aadrm.com, *.informationprotection.azure.com, and *.microsoftonline.com. If any of these are blocked, please share the results with your IT or network team to adjust proxy or firewall settings accordingly. 

2/ Missing or Faulty RMS Client 

Classic Outlook may also require the Microsoft Rights Management Services (RMS) Client 2.1 to properly handle IRM-protected content. If it’s not already installed, you can download it from the official Microsoft Download Center. Please note that administrator rights are required to install this client. 

Download and install the RMS Client 2.1 from Microsoft: Download Rights Management Service Client 2.1 from Official Microsoft Download Center 

3/ Lastly, you may consider asking your IT administrator to review Conditional Access policies in the Microsoft Entra Admin Center. It’s important to ensure that Outlook Desktop is not being restricted and that Multi-Factor Authentication (MFA) settings are not interfering with IRM authentication. In some cases, temporarily disabling MFA for testing purposes can help isolate the issue.  

Since New Outlook and Outlook on the Web are functioning correctly, you may consider using those clients as a temporary alternative while we continue investigating the issue with Classic Outlook.  

Please let me know once you’ve had a chance to review these points, and I’ll be happy to assist with next steps. While our initial response might not always resolve the issue right away, your input and any additional details you can share will really help us work together toward a solution. Your cooperation means a lot, and it helps us ensure that we can deliver the best possible support tailored to your situation. 

Thank you for your patience and your understanding. If you have any questions, please feel free to reach out.  

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Hello,

I am experiencing the same issue. I did go through the suggestions Ruby-N provided above but didn't help in my case.

I am running Outlook classic version 2508 19127.20222.

I have a virtual machine with an older client version, 2502 18526.20168 and opening the encrypted email works as expected. So that leads me to an update to the client broke it.

I have a client that is having the same issue with all of their classic Outlooks. Works in web and new outlook but not in classic outlook. They have been using new outlook or web to open these emails but can't move to new outlook permanently as a solution as they have a third party software they use that will not work with new outlook as of yet.

The worst part of this is if one of these emails is the first email in the inbox or a subfolder - it freezes Outlook as it works through this. It's pretty crippling for them. This is the only comment/question I can find on the issue so far and no solution.

I have the same issue but using semi-annual channel. anyone find a working fix?