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New Outlook Bug Locks Out Excel Files
3 Dec, 2025
Summary
- Outlook users cannot open Excel attachments with non-ASCII characters.
- Microsoft confirmed the issue and is developing a fix.
- The problem has affected users for at least two weeks.
The new Outlook email client is experiencing a significant bug that prevents users from opening Excel attachments containing non-ASCII characters in their file names. This issue, which has persisted for at least two weeks as of December 3rd, 2025, has been confirmed by Microsoft and is identified by service alert ID EX1189359.
Microsoft has stated that the problem arises from a missing encoding in the requests used to open these files. Users attempting to access affected attachments receive a message suggesting they try again later. Major organizations, including the UK's National Health Service, have reported experiencing this frustrating problem.
While Microsoft has confirmed that a fix is being developed and validated, a timeline for its deployment has not yet been announced. This ongoing issue highlights potential vulnerabilities in the new Outlook client's handling of file attachments with special characters, impacting user productivity.
