What If One Accidental Email Cost Your Business Millions?

You hear it all the time – data leaks, security breaches, files being sent to the wrong people. But here’s the part most small business owners don’t want to hear: sometimes, data doesn’t just get lost. It walks right out the door.

In today’s world, data is currency. It’s the lifeblood of your business. And just like you’d never leave cash lying around, you shouldn’t leave your data unprotected either.

Welcome to the world of Data Loss Prevention (DLP) in Microsoft 365 – your digital guard dog that stops your business’s most valuable information from leaking out, whether accidentally or intentionally.

The Unspoken Problem Most Businesses Ignore

As someone who’s worked with companies around the globe on Microsoft 365 setups, I’ve noticed a common trend: many businesses are quick to protect users with MFA, lock down devices with Defender for Business and BitLocker, and set up Conditional Access policies. But they completely overlook protecting the actual data.

That’s like installing locks on every door in your office, but leaving the filing cabinet wide open.

Here’s the good news. If you’re already using Microsoft 365, you’ve got powerful DLP tools at your fingertips – you just need to know how to use them.

So What Exactly Is Data Loss Prevention?

Think of it this way: your business is a bucket, and your data is the water inside. Now imagine there are holes in the bottom of that bucket. That’s your data slipping away – through emails, documents, shared files, and cloud apps.

DLP is what plugs those holes.

It watches over services like Exchange Online, SharePoint, OneDrive and Teams. It can stop someone from emailing sensitive information out of the business – whether by mistake or on purpose. It can block files containing credit card data or national insurance numbers from being uploaded to unauthorised cloud services. And yes, it even works with newer tools like Microsoft Copilot.

The Catch: Licensing

If you’re using Microsoft 365 Business Premium, you already get DLP protection for Exchange, SharePoint, and OneDrive – which is great. But if you want to go deeper – like protecting devices themselves – you’ll need an upgrade to Microsoft 365 E3 or E5.

For this walkthrough, we’re focusing on Business Premium. Let’s keep things accessible.

Not All Data Is Created Equal

Before you can protect anything, you need to know what’s worth protecting. Microsoft calls this Sensitive Information Types. These are the kinds of data that you don’t want getting out – things like credit card details, passport numbers, national insurance numbers, or confidential research.

Here’s where it gets smart: Microsoft 365 already includes 225+ built-in sensitive information types for countries all over the world. In the UK? You’ll find National Insurance numbers and NHS numbers ready to go. But you can also create your own – for example, a law firm might want to protect case numbers, while a hedge fund might want to secure their algorithm.

Inside the Microsoft Purview Portal

This is where the real work begins.

You access DLP and sensitive information types through Microsoft Purview – the hub for all data protection tools. Yes, it can look overwhelming. There’s a lot going on. But once you get to grips with it, it’s surprisingly powerful.

Start by exploring the Classifiers > Sensitive Information Types section. Here you’ll see that list of prebuilt types, and you can begin shaping your DLP strategy around what really matters to your business.

Creating Your First DLP Policy

Now let’s plug some of those holes in your bucket.

Head back to the Data Loss Prevention > Policies section and create a new policy. Microsoft has made this incredibly simple with templates. Since we’re in the UK, we’ll use the UK Financial Data template.

This policy automatically looks for financial data like account numbers and credit card info. You give the policy a name, choose where it applies – Exchange, SharePoint, OneDrive – and who it applies to.

Want to exclude certain teams or sites? You can. Want to get more granular? Absolutely. Microsoft lets you control this at the level of individual users or files. It’s not just a blanket approach.

What About Admin Units?

You might see something called Admin Units pop up. Unless you’ve got an E5 licence, this won’t be available – and that’s fine. Admin Units are designed for huge organisations where you want different teams managing different data sets across departments or regions.

Making It Your Own

Here’s the beauty of it: you’re in control. You can start with a template, keep the default settings, or dive into Advanced DLP Rules and start tweaking things like detection thresholds, user groups, and response actions.

We’ll cover advanced policies in future posts – but for now, starting simple is better than doing nothing.

The Bottom Line

Your business probably isn’t a target for a Hollywood-style cyberattack – but it is vulnerable to something far more common: human error.

A single email with the wrong attachment. A file shared to a personal Dropbox. A junior employee pasting sensitive information into Copilot. These things happen every day – and they cost businesses real money, trust, and time.

So don’t wait until something goes wrong.

Start using DLP in Microsoft 365 today. It’s already there, waiting to help you plug those leaks – and it might just save your business from a very expensive mistake.