Hello Dylan
Microsoft 365 Defender for Office is licensed per user - so each account needs a license. It is included in some licenses -
Microsoft Defender for Office 365 Plan 2 is included in Office 365 E5, Office 365 A5, and Microsoft 365 E5. Microsoft Defender for Office 365 Plan 1 is included in Microsoft 365 Business Premium.
More information is here - https://learn.microsoft.com/microsoft-365/security/office-365-security/microsoft-defender-for-office-365-product-overview?view=o365-worldwide
-- Diane
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