Email Security platforms inspect inbound, outbound, and internal mail flow to block phishing, business email compromise (BEC), account takeover, malicious attachments, and credential-harvesting links. The category has shifted from gateway-mode (SEG) appliances and MX-record redirects to API-integrated architectures that sit alongside Microsoft 365 and Google Workspace, using behavioral, linguistic, and social-graph analysis to identify identity-based attacks that evade signature-based filters. Modern platforms extend beyond email itself into adjacent collaboration surfaces (Teams, Slack) where the same social-engineering payloads increasingly land. Leading vendors include Proofpoint, Abnormal Security, Mimecast, Microsoft Defender for Office 365, Cisco Secure Email, Barracuda, Check Point Avanan, and IRONSCALES.