This browser is no longer supported.
Upgrade to Microsoft Edge to take advantage of the latest features, security updates, and technical support.
![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(128, 8%, 22%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3EA%3C/text%3E%3C/svg%3E)
Since April we started a new EA agreement with Microsoft and added all of our users to E5 licenses of M365 on top of the E3 licenses they already had - we were told that the E3 licenses would disappear anyway.
We don't know if that is related, however since mid-April we started to have numerous users who find their email attachments to get corrupt in Outlook. Whether it's with Outlook 2016 or 365, and Windows 10 or 11 Pro, the symptoms are always the same: the size of the attachments decrease significantly and they cannot be opened in their usual application (Adobe PDF Viewer, Word, Excel, PowerPoint, etc.).
Attachments in emails are oftentimes received already corrupt and are therefore unusable, sometimes they are good to be viewed or opened, then later on get corrupt. Sometimes
the attachments get corrupt when their related emails get forwarded to other users (who also find corrupt attachments in the emails they received).
We noticed that Outlook sometimes get even in a state where no file can get attached to a new email, or no attachment from a received email can get saved on any drive.
Whenever a user tries to open a corrupt attachment, an error message similar to this appear: "there was an error opening this document. The file is damaged and could not be repaired". No useful details get logged in the Event Viewer, all we see at the time of the error is "An unexpected error has occurred".
We tried the SaRa diagnosis program on some users' workstations with no luck, the SaRa program gets to vanish before the issue is seen again.
We tried to run Desktop Outlook in Safe Mode, the issue has not been seen. We tried to disable all of our add-ins one by one in normal mode, the issue was seen with every add-in being disabled....
We have hundreds of users and are out of ideas. Can you please help.
Using Classic Outlook on Windows for personal email, calendar, and contact management
Locked Question. This question was migrated from the Microsoft Support Community. You can vote on whether it's helpful, but you can't add comments or replies or follow the question.
Our Office 365 version is 2303.
We solved the issue here by deploying the following Known Issue Rollback (KIR) to over a thousand of workstations:
Windows 11, version 21H2: KB5023774 230222_032017 Known Issue Rollback
Windows 10, versions 21H2/22H2: KB5023773 230222_032013 Known Issue Rollback
Extract from the explanations:
"After installing KB5023773 or later updates, you might have intermittent issues saving, or copying, or attaching files using 32-bit apps which are large address aware and using the CopyFile API. Windows devices are more likely to be affected by this issue when using some commercial/enterprise security software which uses extended file attributes. We are not receiving reports that copying files using File Explorer is affected, but CopyFile API used within apps might be affected."
That very much looks related to me.
Our early testing has identified that if KB5026513 is uninstalled followed by a restart, PDFs can be opened without an issue. 3 Microsoft engineers we have spoken to did not know whether any KB was the cause of the issue. process was we ran in all May updates and then took KB5026513 out.
Hi Stephane,
How did your testing go with this? Did you follow microsoft's KIB process to resolve this issue ?
We are in this process right now. We cannot say for sure now that this fixed the problem as it occurs every once in a while, but we will have our most affected users with the fix working from today, so we will see, I will report back here.