After recently working with Sophos Advanced Support (Issue #8207900) it became clear that the current DLP protection available in Sophos Central/Endpoint Protection does not fully block attachments containing prohibited content from being copied/pasted or dragged/dropped into Outlook 2016 email messages. However, the protection does work when using the Attach File feature and browsing to an attachment. Having DLP protection work only partially with Outlook 2016 isn't acceptable and should be fixed as soon as possible. I work for a large MSP and we and our customers have important compliance needs like PCI-DSS that need to be satisfied. We are a Platinum partner with Sophos and would rather use Sophos' DLP protection but for the time being, this limitation has prompted us to consider implementation of other vendor solutions like Microsoft's DLP protection. I've been informed that the fix for this issue is on the development roadmap and will be included with future updates/enhancements but because of current/urgent regulatory compliance activity across the industry, recommend strongly that resolution for this issue be moved up in your development/product management scheduling.