New Outlook Glitch Prevents Excel Attachments

Users of the new Outlook for Windows are facing a problem where Excel attachments won’t open if their filenames include non-standard characters.

The issue, logged under EX1189359, presents a generic error telling users to “Try opening the file again later,” making it unclear why the attachment fails.

This bug appears exclusively in the new Outlook client, while the classic version remains unaffected. Microsoft has identified the root cause as an encoding problem in the file request process.

Files containing accented letters, symbols, or characters from non-English scripts are not processed correctly, causing immediate failures when attempting to open them.

Reports suggest that this issue has persisted since late November 2025, affecting mainly users and organizations that frequently handle Excel files with international or complex filenames.

Microsoft’s Response and Fix

As of December 1, 2025, Microsoft has created a fix for the Excel attachment issue in the new Outlook for Windows. The update is still being tested and isn’t available to everyone yet.

Microsoft is also looking into why the problem happened to prevent it from happening again. A new status update is expected later on December 1, UTC.

Workarounds until the fix is available:

Use Outlook on the Web (OWA): The web version opens these attachments correctly.
Download the File First: Save the attachment to your computer and then open it in Excel to avoid the error.

This issue highlights ongoing challenges with the new Outlook client, which some users feel is missing features compared to the classic version. Admins can track the fix in the Microsoft 365 admin center under EX1189359.