Sometimes, together with attachments, a file with the name in question is also present in the email, the content of this file looks like this:
QuickSand disarmed file "EIZODUI_LS_0112921999_E500000260.pdf"
QuickSand disarmed file "EIZODUI_LS_0112923698_E500000233.pdf"
What is quicksand?
Office documents and PDF files can contain active content, for example PDF files can contain and execute JavaScript commands or Office documents that contain PowerShell scripts, QuickSand Sandbox is able to locate and remove "Active" content from Office files and PDF.
Basically the file warns that the attachments have been "disabled" in those functions that could potentially be a danger, this sometimes leads (rarely) to not make any files that use markings or scripts work correctly but make the files "safe".
