The Attachment Manager is included in Windows to help protect your PC from unsafe attachments that you might receive with an e-mail message and from unsafe files that you might save from the Internet. If the Attachment Manager identifies an attachment that might be unsafe, the Attachment Manager prevents (blocks) you from opening the file, or it warns you before you open the file.
It uses the IAttachmentExecute application programming interface (API) to find the file type, to find the file association. When one of these applications saves a downloaded file on a disk formatted with NTFS, then it updates the metadata for the file with the zone it was downloaded from. The metadata is saved as an Alternate Data Stream (ADS). If you wish to unblock a downloaded file, you can do so by right-clicking it, selecting Properties and clicking on Unblock.
The Open File – Security Warning prompt is a security measure that will ask for your permission before opening a file on your PC that came from an unknown source such as the Internet or another PC.
Windows SmartScreen helps keep your PC safer by warning you before running unrecognized apps and files downloaded from the Internet.
Open File – Security Warning and Windows SmartScreen automatically blocks these types of apps and files until you unblock them.
If you like, you can add Unblock to the context menu of files and folders to make unblocking files easier as needed.
When you click on Unblock in the context menu of a blocked file, you will be prompted by either a Open File – Security Warning or Windows Defender Smartscreen dialog to approve unblocking the file without opening or running the file.
When you click on Unblock in the context menu of a folder, you can select to Unblock files only in this folder or Unblock files in this folder and subfolders. You will not get prompted by a Open File – Security Warning or Windows Defender Smartscreen dialog to approve.
This tutorial will show you how to add or remove an Unblock file context menu to files and folders for all users in Windows 10.