We want to block ALL file extensions and default them into quarantine. Is there a real easy&simple way like a wildcard?
Will the new Sandboxing feature, coming in v.9.4 (out in beta now), alleviate your concerns? Or are you trying to embargo all attachments for reasons other than potential malware?
Sandstorm has not impressed me yet in beta neither i believe it will be THE solution to all problems with crypto-trojans and other stuff.
---
Sophos UTM 9.3 Certified Engineer