One of the security services included with Microsoft 365 Business Premium is Microsoft Defender for Office 365 Plan 1.

Purchased separately, Defender for Office 365 Plan 1 typically costs around $2 per user per month, but it is already included as part of the Business Premium license.

Despite that, many organizations continue to run third-party email security platforms such as:

  • Barracuda
  • Mimecast
  • Proofpoint

These systems are often deployed as external email gateways designed to filter malicious email before it reaches the user.

What many IT teams don’t realize is that Microsoft Defender for Office 365 provides many of the same protections directly within the Microsoft 365 platform.

Email Link Protection

Defender for Office 365 scans links embedded inside email messages.

When a user clicks a link, Microsoft checks the destination in real time to determine whether it leads to a malicious website.

If the link is determined to be unsafe, the connection is blocked before the user can access the site.

This helps protect users from phishing attacks and malicious websites delivered through email.

File Detonation and Zero-Day Threat Protection

Defender for Office 365 also performs file detonation, a technique used to identify unknown threats.

Attachments that pass through traditional antivirus scanning can be executed in a secure sandbox environment where their behavior is analyzed.

If the file behaves suspiciously, it is flagged or blocked before the user can access it.

This capability helps detect zero-day threats that traditional signature-based scanning might miss.

Protection Beyond Email

Another important capability is that Defender for Office 365 protection extends beyond just email attachments.

Files uploaded by users into OneDrive, Microsoft Teams, or SharePoint can also be scanned and analyzed.

This helps ensure that malicious files do not spread through collaboration platforms within the organization.

Integrated Security Inside Microsoft 365

Because Defender for Office 365 operates directly inside the Microsoft 365 environment, it integrates with other security services such as:

  • Microsoft Defender
  • Microsoft Intune
  • Microsoft Entra ID (Azure Active Directory)

This allows email security to function as part of a broader Microsoft 365 security architecture, rather than as a separate gateway system managed by a third-party vendor.

For many organizations, this means the email security platform they need is already included in the Microsoft 365 environment they are paying for.

Learn More

If you're evaluating how Microsoft Defender, Intune, and Entra ID work together to secure modern IT environments, you may want to review our overview of Microsoft 365 security architecture: https://www.xerillion.com/microsoft-365-it-security-modernization/?