This talk presents a comprehensive analysis of TLS in the SMTP world. We scanned over 20 million unique email recipient domains and analyzed TLS (X.509) certificates to measure overall STARTTLS deployment quality. We discovered a wealth of information that was previously unknown. The analysis will provide a good baseline in terms of STARTTLS and TLS certificates used in SMTP.
Scan tool: https://prbinu.github.io/tls-scan