Cloudflare Email Security customers using Microsoft Outlook can now enhance their data protection using our new DLP Assist capability. This application scans emails in real time as users compose them, identifying potential data loss prevention (DLP) violations, such as Social Security or credit card numbers. Administrators can instantly alert users of violations and take action downstream, whether by blocking or encrypting messages, to prevent sensitive information from leaking. DLP Assist is lightweight, easy to deploy, and helps organizations maintain compliance without disrupting workflow.
Making DLP more accessible
After speaking with our customers, we discovered a common challenge: many wanted to implement a data loss prevention policy for Outlook, but found existing solutions either too complex to set up or too costly to adopt.
That’s why we created DLP Assist to be a lightweight application that can be installed in minutes. Unlike other solutions, it doesn’t require changes to outbound email connectors or provide concerns about IP reputation to customers. By fully leveraging the Microsoft ecosystem, DLP Assist makes email DLP accessible to all organizations, whether they have dedicated IT teams or none at all.
We also recognized that traditional DLP solutions often demand significant financial investment in not just software but also in team members to configure and monitor them. DLP Assist aims to eliminate these barriers. Customers can use the application as part of our Email Security product, avoiding the need for additional purchases. Plus, with our DLP engine powered by optical character recognition (OCR), confidence levels, and other detection mechanisms, organizations don’t need a dedicated team to constantly oversee it.
By eliminating the complexities of legacy DLP and email systems, we allow customers to quickly begin preventing the unauthorized egress of sensitive data. With DLP Assist, organizations can be confident in controlling and protecting the information that leaves their environment.
How does it work?
Our DLP Assist is an application that integrates with the Desktop (Mac and Windows) and Web Outlook clients, passively scanning emails as they are composed. Running in the background within Microsoft Outlook, DLP Assist continuously monitors new text and attachments added to emails that users are drafting.
When a customer downloads and installs the application, Cloudflare creates a unique client ID specifically for emails read from the DLP Assist application, which serves as an identifier solely for use by DLP Assist within Cloudflare’s backend. When a user begins drafting a message, the DLP Assist application invokes several Microsoft Outlook APIs to gather information about how the message is changing. These APIs let the Cloudflare application continuously access different parts of the message like subject, body, attachments, etc. While the application is reading the changes within the message, it also establishes a secure, encrypted connection with a Cloudflare Worker.
As raw data about the email and attachments is sent to the Worker, the Worker relays the information to our DLP engine, which is at the heart of our scanning process. It leverages OCR technology to analyze attachments, extract text from images, and detect DLP violations across both email content and embedded data. It also examines raw text to ensure a comprehensive analysis of every part of the email and its attachments. While our engine supports most attachment types, it currently does not process video or audio files.
The DLP engine runs on all of our servers, and we also store the customer DLP profile configuration data on all of our servers. By keeping DLP policy configuration data on all servers alongside our analysis engine, we eliminate the need to reroute requests across our network allowing for low-latency, real-time DLP checks. The customer's client ID enables us to find and apply their defined DLP profiles and accurately determine policy violations, delivering results directly to the Cloudflare Worker. If a violation is found, the Worker responds to the application to take action within Outlook.
Our architecture ensures real-time scanning with minimal latency, as end users are always near a Cloudflare Worker, regardless of their location. Additionally, this design provides built-in resilience — if a Cloudflare Worker becomes unavailable, another can take over, allowing for uninterrupted DLP enforcement. By scanning in real time, this allows us to provide immediate feedback to the user about any DLP violations that they have within their email, rather than the user having to wait till the message has been sent.
If a violation is detected, the application first displays an insight message — a ribbon notification at the top of the email — alerting the user to the issue. Administrators have full control over this message and can customize it to provide specific guidance or warnings. We find that most of our customers point users to documentation reminding them what is allowed to be sent outside of the organization.
When a DLP violation occurs, DLP Assist also injects a header into the EML file to indicate the violation. If the user removes the content that is in violation, the header is automatically removed as well.
If the violation remains unchanged, DLP Assist invokes a Microsoft Outlook API which prompts the user with a final warning, giving them another opportunity to revise the message before sending.
If the user proceeds without making changes, the email will be sent from the client with headers embedded into the EML showing that message contains a DLP violation. Organizations can configure their outbound mail transfer agent (MTA) to take appropriate action based on these headers. For those with Microsoft as their outbound MTA, Cloudflare’s DLP Assist integrates with Microsoft Purview, enabling organizations to block, encrypt, or require approval before sending.
For example, if an organization configures Purview to block the email, users will receive a notification similar to this one.
Violations detected by the DLP Assist application can also be sent externally through our Logpush feature. Customers have the flexibility to integrate this data with SIEM or SOAR platforms for deeper analysis, or store it in bucket storage solutions like Cloudflare R2. Additionally, customers can enhance their reporting capabilities by viewing block data directly within their outbound gateway.
As we continue to improve our DLP engine, we're introducing more advanced ways to analyze messages. During Security Week 2025, we’re unveiling new AI methodologies that automatically fine-tune DLP confidence levels using machine learning models. Initially, these enhancements will be rolled out for Gateway violations, but we plan to extend them to email scanning in the near future. For more details, see the associated blog post.
Cloudflare One’s DLP Assist is designed for quick deployment, enabling organizations to implement a data loss prevention solution with minimal effort. It allows customers to immediately begin scanning emails for sensitive data and take action to prevent unauthorized sharing, ensuring compliance and security from day one.
How can I start using it?
To get started, navigate to the Zero Trust dashboard and click on the Email Security tab. From there, select the Outbound DLP tab.
To install DLP Assist, organizations can download the manifest file, which provides Microsoft with the necessary instructions to install the application within Outlook. Administrators can then upload this manifest file by going to Integrated Apps within the Microsoft 365 Admin Center and selecting Upload Custom Apps:
This application is best suited for use with OWA (Outlook Web Access) and the desktop (Mac and Windows) Outlook client. Due to Microsoft limitations, a stable experience on mobile devices is not yet available.
More information can be found within our developer documentation.
What's next?
We’re continuously expanding our solutions to help organizations protect their data. Exciting new DLP and Email Security features are on the way throughout 2025, so stay tuned for upcoming announcements.
To learn more about our DLP and Email Security solutions, reach out to your Cloudflare representative. Want to see our detections in action? Run a free Retro Scan to uncover any potentially malicious messages hiding in your inbox.