Microsoft has acknowledged a irritating new problem affecting customers of the “new Outlook” for Home windows, the place Excel attachments fail to open if their filenames include non-ASCII characters.
The technical glitch, tracked below the reference ID EX1189359, triggers a obscure error message advising customers to “Strive opening the file once more later,” leaving many confused about the reason for the blockage.
The issue targets the trendy “new Outlook” shopper explicitly and doesn’t seem to affect the traditional model of the software program. In keeping with Microsoft’s service well being dashboard, the foundation trigger lies in an encoding error inside the request used to open the recordsdata.
When an Excel file hooked up to an e mail consists of non-standard characters comparable to accented letters, symbols, or non-English scripts, the appliance fails to course of the filename accurately, leading to a right away error.
This problem has been ongoing since late November 2025, with preliminary experiences surfacing round November 23. Whereas the scope is proscribed to particular file naming conventions, the affect is critical for worldwide customers or organizations that continuously use non-ASCII characters in doc titles.
Microsoft’s Response and Repair Standing
As of the most recent replace on December 1, 2025, Microsoft engineers have efficiently developed a repair to deal with the lacking encoding in file-handling requests.
Nevertheless, the answer shouldn’t be but accessible to all customers. The corporate is presently within the validation section, testing the deployment to make sure it resolves the error with out introducing secondary points.
Microsoft can also be investigating why this encoding error occurred within the first place to forestall related regressions in future updates. An additional standing replace is anticipated by the night of December 1, UTC time.
Till the patch is totally rolled out, Microsoft has offered two official workarounds for customers who want fast entry to their spreadsheets:
Use Outlook on the Internet (OWA): The net-based model of Outlook accurately processes these attachments, bypassing the client-side encoding failure.
Obtain the File Regionally: Customers can save the attachment to their pc first. As soon as the file is saved to an area drive, it may be opened immediately in Excel with out triggering the Outlook previewer error.
This incident joins a rising listing of pains for the brand new Outlook shopper, which has confronted scrutiny from energy customers for feature-parity gaps in comparison with the traditional COM-based software. Admin directors can monitor the progress of the repair within the Microsoft 365 admin heart below EX1189359.
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