Office 365 Advanced Threat Protection (ATP) is Microsoft's optional cloud-based service that scans and filters email to protect subscribers from malware in attachments and hyperlinks to malicious websites.
Follow these steps to enable:
Log in to the Microsoft 365 admin center.
Go to the Security & Compliance Center.
On the left navigation menu, click Threat management, and then click Threat protection.
Click Advanced Threat Protection.
Click Manage settings.
On the ATP settings page, turn on the feature that you want to use, such as:
Safe Attachments: blocks email messages with attachments that contain malicious content.
Safe Links: blocks users from accessing malicious links in email messages.
Click Save changes.
To ensure that ATP is working correctly, you can send test email messages to yourself and verify that they are properly protected.