Attached files from Outlook 2013/2019 on Windows Server 2016 are blocked when downloaded. "This file came from another computer..."

Question

I have a virtual machine with W. Server 2016 Std. to which several users connect via RDP.

Some of these users are having problems downloading any type of attachments from Outlook; when they download a file, it gets blocked, and the typical message

"This file came from another computer and might be blocked to help protect this computer"

appears in the file properties. However, when you double-click on the attachment in Outlook, it opens without any problem in read-only mode, and the file generated under C:\Users\username\AppData\Local\Microsoft\Windows\INetCache\Content.Outlook\0WI918ZZ is blocked too. This problem is also experienced by new users created on the server.

Proposed solutions that I have found and tested so far:

• Add the registry key "SaveZoneInformation=1" Image
• Do not preserve zone information in file attachments GPO enabled.
• Cloned the VM and upgraded Outlook 2013 to a slightly newer version (Outlook 2019) but the problem persists.
• Uncheck/Check Turn off Attachment Preview in Outlook 2013
• Disable Protected view for outlook attachments in Trust Center https://i.sstatic.net/SjPfL.png

System information: Windows Server 2016 Standard Outlook 2013 15.0.4420.1017 / Outlook 2019 last version. Domain: No (workgroup). RDS roles.

Answer 1

Windows classifies certain files as unsafe downloads and attachments by identifying the files type and the security settings for each file. For doing this, it uses the Attachment Manager in Windows, which is a service that gets activated whenever you receive an e-mail message with an attachment and from unsafe files that you might save from the Internet.

You can disable the Attachment Manager using Windows Registry, refer to this article:How to Fix “This File Came From Another Computer And Might be Blocked” Error