Microsoft 365 Email Security for Law Firms: How One Law Firm Got Spoofed and What I Did to Fix It

The Email Spoofing Incident That Triggered a Security Overhaul

A small law firm in Northern Virginia was using Microsoft 365 and believed their email was secure. They had purchased their licensing, enabled two-factor authentication, and set up an SPF record. On the surface, everything appeared to be fine.

However, clients and other law firms soon began receiving suspicious emails that appeared to be coming from the firm's official email address.

These messages included malicious links and false requests. Some even mimicked the tone and structure of the firm’s legitimate communication. Fortunately, one recipient flagged it before anyone interacted with the content. That is when the firm contacted me for help.

This case is a prime example of why Microsoft 365 email security for law firms is crucial and why default settings alone are insufficient to prevent impersonation or spoofing threats.

Why Microsoft 365 Email Security for Law Firms and Small Businesses Is Often Overlooked

This is not just a law firm problem. I regularly see the same issue in trades, service-based companies, and nonprofits.

Most of these businesses believe they are secure because they have two-factor authentication enabled and an SPF record set up. But those are only basic steps. Without DKIM, DMARC, and Microsoft Defender being configured, Microsoft 365 cannot verify whether an email claiming to come from your business is genuine or not.

Many business owners are unaware of these protections. Worse, many IT providers do not set them up by default.

What I Found Missing in Their Microsoft 365 Setup

When I reviewed the firm’s Microsoft 365 tenant, I found several important security features had never been configured:

• Microsoft Defender for Office 365 was not enabled

• DKIM and DMARC were missing entirely

• Their SPF record existed but was not properly enforced

• No impersonation or phishing policies were active

• Mailbox Intelligence was not enabled

• Logins were not restricted by location, so anyone could attempt to access their accounts from anywhere in the world.

The firm had the right tools available but was missing the configuration that makes those tools effective.

Here’s How I Secured Their Environment

To stop spoofing and prevent future threats, I made the following changes:

1. Enabled Microsoft Defender for Office 365 Plan 1

This activated phishing protection, safe link scanning, malware detection, and impersonation alerts.

2. Configured DKIM and DMARC

I added the correct DNS records and enabled domain signing to verify that the outgoing email was legitimate.

3. Corrected and Enforced SPF

I updated their SPF record to match Microsoft’s best practices and ensured it was enforced to block unauthorized messages.

4. Set Up Impersonation Protection

I created policies to protect common mailboxes, such as info@ and billing@. I added user-level impersonation protection using Mailbox Intelligence, which utilizes AI to detect when someone is attempting to mimic real users within the organization.

5. Activated a 90-Day Microsoft Defender Plan 2 Trial

This provided the firm with access to advanced features, including real-time threat detection, automated investigation tools, and attack simulation training.

6. Restricted Account Access by Country

I limited login access to users located in the United States. This adds another layer of protection by blocking unauthorized access attempts from outside the country.

What Is Mailbox Intelligence and Why Does It Matter?

As part of Microsoft Defender’s impersonation protection, I enabled Mailbox Intelligence, which uses machine learning to understand typical communication patterns between your team and their contacts. When an attacker attempts to send a message that appears to originate from someone within your business, this AI-powered tool can identify the difference.

It does not rely only on display names. It examines how your team typically communicates and flags messages that do not conform to the pattern. This helps catch advanced impersonation attempts that other filters might miss.

Microsoft 365 Is Not Secure by Default

Many small businesses assume Microsoft 365 is automatically secure once it is purchased. In reality, Microsoft provides excellent security tools, but they must be configured manually.

If email authentication is not set up, if Microsoft Defender is not enabled, or if login access is open to the world, your business may be vulnerable to spoofing, phishing, and unauthorized access.

Why SPF, DKIM, and DMARC Are So Important

These three records work together to protect your domain’s reputation and prevent forged emails:

• SPF authorizes specific servers to send emails for your domain.

• DKIM adds a digital signature to verify the content and the sender.

• DMARC tells receiving servers how to handle messages that fail SPF or DKIM checks

When all three are configured and aligned, spoofed messages pretending to come from your business can be blocked before they ever reach someone’s inbox.

Think You Are Protected? You Might Want to Double-Check

Even if you are using two-factor authentication and have a working SPF record, that is only part of the picture. Most spoofing attacks happen outside of your user accounts. That is why it is so essential to secure your domain and email flow properly.

If these protections were never configured during your Microsoft 365 setup, your business may still be vulnerable.

I Provide Microsoft 365 Security Services Across the Mid-Atlantic

I work with small to mid-sized businesses throughout Northern Virginia, Washington DC, Pennsylvania, West Virginia, Delaware, and select areas of Maryland. Whether you're a one-person law firm, a business just getting started with five employees, or a growing team of fifty, I can help secure your Microsoft 365 environment with modern protections that's often overlooked or misconfigured.

My Microsoft 365 Security Services Include:

• SPF, DKIM, and DMARC configuration

• Microsoft Defender setup and policy management

• Mailbox Intelligence and impersonation protection

• Country-based login restrictions

• Defender Plan 2 trial activation and support

• Ongoing monitoring and practical user support

  
  

Book Your Microsoft 365 Security Checkup

If you are unsure whether your environment is secure, let’s take a look together. I offer straightforward audits with actionable recommendations.

Let’s ensure your email system is protecting your clients, staff, and business reputation.