What port is used for SMTP over SSL/TLS (SMTPS)?

What port is used for SMTP over SSL/TLS (SMTPS)?

• A. 465
• B. 25
• C. 22
• D. 513

Answer: (A)

SMTPS uses encryption from the moment you connect, so TLS is established immediately without upgrading an existing connection. That immediate, implicit TLS is why a dedicated port is used for SMTPS. Historically this is port 465, which was assigned for SMTPS to handle an encrypted SMTP session right at connect. In contrast, standard SMTP on port 25 (and the submission port 587) typically starts unencrypted and upgrades to TLS later using STARTTLS. So the port associated with SMTPS is 465. The other listed ports serve different purposes: 25 is plain SMTP (or SMTP with STARTTLS), 22 is for SSH, and 513 is not used for SMTP.

SMTPS uses encryption from the moment you connect, so TLS is established immediately without upgrading an existing connection. That immediate, implicit TLS is why a dedicated port is used for SMTPS. Historically this is port 465, which was assigned for SMTPS to handle an encrypted SMTP session right at connect. In contrast, standard SMTP on port 25 (and the submission port 587) typically starts unencrypted and upgrades to TLS later using STARTTLS.

So the port associated with SMTPS is 465. The other listed ports serve different purposes: 25 is plain SMTP (or SMTP with STARTTLS), 22 is for SSH, and 513 is not used for SMTP.