How can i fix error: Mail system failure. Check your mail installation

Hi @Nakaranee, Disha,

Thank you for posting your question in the Microsoft Q&A forum.

Based on your sharing, this error occurs because the New Outlook does not support the MAPI integration that Classic Outlook uses for sending files directly via email. Therefore, even if you switched to New Outlook, Excel still needs to use MAPI method and since New Outlook doesn't support MAPI, the error message pops up.

I've also tested in my current desktop app. When I use the option "Attach a copy of Excel workbook instead", classic Outlook will automatically open and prepare a file for sending because classic version fully supports MAPI. When I delete classic Outlook completely and use New Outlook only, I received the same error code as you did.

Therefore, if you want to share files from Excel, there are some workarounds you can try using instead:

1- Upload your file to your OneDrive and share the link to the recipient

2- Save a copy manually in your local desktop and then attach it into Outlook emails

3- Revert to Classic Outlook

To revert back to classic Outlook, you can follow this guideline:  

Option 1: Use the built-in toggle if available  

• Open New outlook and look for the toggle switch at the top right corner if this option is available in your app.   
• After turning off the New Outlook toggle switch, you can launch the Outlook (classic) app  

Option 2: Using Windows Registry  

• Press Win + R, type regedit, and press Enter.  
• Then navigate to: HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Preferences   
• Find the key UseNewOutlook > double-click it and set the Value data to 0 > close the registry and restart your computer  

Option 3: Uninstall New Outlook and download classic version.  

• Go to settings > apps > installed apps > find New Outlook and uninstall it  
• Go to this official Microsoft link to download classic Outlook

While New Outlook does not currently support MAPI integration, we’re optimistic about future enhancements. If this feature would improve your workflow, I encourage you to share your feedback directly with the Microsoft engineering team via the Outlook (new) · Community portal. This is the most effective way to ensure your voice reaches the product team and can be considered for future improvements. Your input plays a vital role in shaping the future of Microsoft products.  

Note: As community moderators, we kindly ask for your understanding that our access to internal development details is limited. Our primary role is to guide users toward the appropriate resources and support channels. While we may not have influence product design decisions and have limited access to internal development details, we’ll continue doing our best to support you within the scope of our responsibilities.    

Once you've submitted your feedback, feel free to share the link here in the comments. I’ll be happy to upvote it to help bring more visibility.   

Additionally, since many other users have expressed similar concerns but may not know where to submit feedback, if my response has helped you better understand the situation and guided you toward a possible next step, please mark it as the “Accepted Answer.” Your action will help pin this post to the top, making it easier for others in the community who are experiencing the same issue to find your feedback and support it.   

Thank you again for your time and for raising this important usability concern.

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".    

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