openssl s_client -connect smtp.example.com:465

Category: Mail Servers & Postfix

openssl s_client -connect smtp.example.com:465

Check TLS on the implicit SMTPS port

Connects to the legacy implicit-TLS SMTP port, where encryption starts immediately without STARTTLS. Prints the presented certificate and negotiated cipher. Most modern servers use 587 with STARTTLS instead, but 465 still accepts mail.
Looking for more? Search all 7,657 commands — works offline, in English or Spanish, and fixes typos.