What is SMTPS?

SMTPS (SMTP Secure) is the practice of sending email over SMTP through a connection that is encrypted with TLS/SSL from the very start. Historically tied to port 465, SMTPS wraps the entire SMTP session in encryption — so the sender, recipients, message body, and login credentials never travel in plaintext.

How SMTPS works

With SMTPS, the client opens a TLS-encrypted connection immediately — known as implicit TLS — before any SMTP commands are exchanged, typically on port 465. That differs from STARTTLS, which begins in plaintext on port 587 and upgrades to encryption on request. Once the secure channel is established, the email is transmitted normally, but protected across the whole transit path.

SMTPS vs STARTTLS — and why it matters

SMTPS (implicit TLS, port 465) and STARTTLS (explicit TLS, port 587) both encrypt SMTP traffic; the difference is when encryption starts. Modern mail servers support both, and either one keeps credentials and content private in transit. Mailpro's SMTP relay uses TLS 1.3 from Swiss private infrastructure. Compare port 465 vs port 587 or see which SMTP port to use.

Need reliable, encrypted email delivery? Send through Mailpro's Swiss SMTP relay with TLS built in.