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Threat Intelligence Report

One Blank Field Bypasses Direct Send Control

๐Ÿ“… September 3, 2026 ๐Ÿ“ฐ reliaquest.com ๐Ÿ” 0 CVE(s) referenced

Attackers can bypass Microsoft 365's RejectDirectSend control by sending emails with an empty SMTP envelope sender, allowing unauthenticated phishing messages that appear internal to reach users and highlighting the urgent need for layered email defenses beyond this control.

unclassified

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