Email Spoofing with SMTP Smuggling: How the Shared Email Infrastructures Magnify this Vulnerability

SMTP smuggling is a critical vulnerability allowing email spoofing that bypasses standard authentication protocols like SPF and DMARC. This research presents a large-scale study on its prevalence, uncovering widespread issues due to shared infrastructure and incomplete patches, and introduces a novel, non-intrusive methodology for ethically testing private email services.