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 Attachment Manager classifies files that you receive or that you download based on the file type and the file name extension. Attachment Manager classifies files types as high risk, medium risk, and low risk.
If you like, there is a Do not preserve zone information in file attachments policy that allows you to manage whether Windows marks file attachments with information about their zone of origin (such as restricted, Internet, intranet, local). If this policy is enabled, it will effectively disable downloaded files from being blocked.
This tutorial will show you how to enable or disable blocking files downloaded from the Internet for all or specific users in Windows 11.