To block incoming emails in Proxmox Mail Gateway that contain attachments with a specific extension, for example, .cab I recommend blocking both the extension (MIME type) and the filename (files that end with .cab).
To do this first log in to Proxmox Mail Gateway and under Mail Filter > What Objects > Dangerous Content add the following:
Content Type Filter: extension name (e.g. .cab)
![How to block / quarantine extensions in Proxmox Mail Gateway image 19 - How to block / quarantine extensions in Proxmox Mail Gateway](https://i0.wp.com/pcx3.com/wp-content/uploads/2022/01/image-19.png?resize=415%2C170&ssl=1)
Match Filename: extension name (e.g. .cab)
![How to block / quarantine extensions in Proxmox Mail Gateway image 20 - How to block / quarantine extensions in Proxmox Mail Gateway](https://i0.wp.com/pcx3.com/wp-content/uploads/2022/01/image-20.png?resize=423%2C176&ssl=1)
So afterwards the Dangerous Content object should look like this:
![How to block / quarantine extensions in Proxmox Mail Gateway image 21 - How to block / quarantine extensions in Proxmox Mail Gateway](https://i0.wp.com/pcx3.com/wp-content/uploads/2022/01/image-21.png?resize=736%2C311&ssl=1)
After setting this extension and file name in the What objects section, the default action is to still deliver the emails but without the blocked attachment:
To quarantine or block emails containing these extensions, modify the Mail FIlter > Block Dangerous Files rule and add the Quarantine or Block action depending on the desired action.
![How to block / quarantine extensions in Proxmox Mail Gateway image 24 - How to block / quarantine extensions in Proxmox Mail Gateway](https://i0.wp.com/pcx3.com/wp-content/uploads/2022/01/image-24.png?resize=432%2C546&ssl=1)
After that any emails that contain this extensions will be quarantined: