You have a Microsoft 365 E5 subscription that contains a domain named contoso.com. You deploy a new Microsoft Defender for Office 365 anti-phishing policy named Policy1 that has user impersonation…

'Enable domains to protect' is for protecting specific domains from being impersonated, not for allowing a legitimate external sender who happens to have a similar name to a protected user.

Configuring the 'Phishing email threshold' setting adjusts the aggressiveness of phishing detection but does not specifically address the issue of legitimate external senders being mistakenly identified as impersonators of an internal user.

'Configure which users to protect' is about specifying which internal users are targeted for impersonation protection, not about allowing external senders with similar names.

Enabling Mailbox Intelligence in an anti-phishing policy helps to distinguish legitimate senders from impersonators by understanding the user's communication patterns and frequent contacts. This allows the system to recognize '[email protected]' as a trusted contact, preventing false positives for impersonation against '[email protected]'.