The DocuSign Detection Gap: Why Signature-Based Email Security Fails Against Modern Impersonation Attacks

DocuSign impersonation has become the most common advanced email attack bypassing Microsoft E3/E5 and top secure email gateways. StrongestLayer analyzed 2,500+ real attacks that evaded enterprise defenses in Q4 2025 and found that DocuSign-themed threats made up 13.8% of them. These attacks are highly variable, with an average Jaccard similarity score of just 0.458, meaning signature-based detection fails because no two attacks look alike. Nearly 38% show signs of AI generation, allowing attackers to mass-produce unique variants that evade pattern matching entirely. Document-heavy industries—legal, pharma, financial services, and real estate—are disproportionately at risk. The report concludes that organizations must shift from signatures to reasoning-based detection that evaluates intent and business context rather than static patterns.