We are having an issue where attaching files to email is broken in a way we can't quite get a handle on. It originally started in Outlook 2019 clients. When a user would try to attach a file the error would state:
Our work around, which lasted about three days, was to use the O365 webmail to send emails. Then the same thing started happening there with the same error message.
Some other users are having issues when they open attached files:
Sometimes the attachment will come through with a file size of 0kb, sometimes its just corrupted.
In an effort to isolate the issue, we have tried a number of things.
Outlook in safe mode
Disable all add-ons
Attach file in gmail or other webmail
System file check (sfc /scannow)
Repair on outlook and office files
Removing and re-building the Outlook Profile
It doesn't effect all users and the users it does effect, it doesn't effect all files. None of the above steps changed the issue. We are all quite confused, especially considering it effects all webmail clients, not just Office or O365.