Glossary · Protocol

SMTPS

Simple Mail Transfer Protocol Secure

In plain language

Email sending over a locked connection, so the message cannot be read on the way to the next mail server.

The metaphor

Like the mail carrier driving a locked truck: the letter reaches the post office and nobody along the road can open the bag.

Going deeper

How it works

It is the ordinary mail-sending protocol wrapped in encryption.
Port 465 uses the lock from the start; port 587 starts plain and upgrades to a lock.
Scanners, printers and apps often need this setting chosen correctly.
Major mail providers refuse unprotected connections.

What can go wrong (example scenario)

A scanner was set to send scans to email without encryption. The mail provider rejected every message until the setting was switched to the locked option.

In practice

A printer sends scans to email using the provider's locked server settings.
An invoicing app sends mail through a company mailbox over a locked connection.
A mail test tool reports that the connection is protected.

A question owners ask

Which port should an app use?

Use the provider's published settings. Port 465 with SSL/TLS or port 587 with STARTTLS are the usual pair.

Related terms

Something here sounds like your problem?

Every WILDCARD card exists to solve one named problem. Find yours.

Pick your problem →