SMTPS (Simple Mail Transfer Protocol Secure) is a secure variant of SMTP that uses SSL/TLS encryption to protect the communication between mail servers. Here’s a brief history of SMTPS:

1. Introduction of SSL/TLS: In the mid-1990s, Netscape Communications developed SSL (Secure Sockets Layer) as a security protocol to provide encryption and authentication for web communications. SSL was later succeeded by TLS (Transport Layer Security) as the standardized protocol.
2. SMTPS as an extension: To secure SMTP communication, the concept of SMTPS emerged as an extension of SMTP. SMTPS utilized SSL/TLS to establish a secure and encrypted channel between mail servers, ensuring the confidentiality and integrity of email transmission.
3. Encryption with SSL/TLS: SMTPS involved establishing an SSL/TLS connection before the SMTP communication began. The SSL/TLS handshake process enabled the negotiation of encryption algorithms, secure key exchange, and the establishment of a secure connection between the client and server.
4. Transition to STARTTLS: Although SMTPS provided a secure option for email transmission, it was gradually replaced by a different approach known as STARTTLS. Instead of using a separate port for secure communication, STARTTLS allowed the encryption to be initiated within the standard SMTP protocol.
5. STARTTLS adoption: STARTTLS is an extension command added to SMTP that enables a plain-text SMTP session to be upgraded to an encrypted TLS session. By supporting opportunistic encryption, STARTTLS made it possible for servers to advertise the availability of TLS encryption and establish secure communication with compatible servers.
6. Widespread use of STARTTLS: The use of STARTTLS with SMTP became widely adopted as it provided a more flexible and interoperable approach to securing email transmission. It allowed servers to support both encrypted and non-encrypted connections on the same port, and it facilitated easier integration of encryption into existing SMTP infrastructure.

As a result, SMTPS is less commonly used today, and the industry standard for secure email communication is to use STARTTLS with SMTP. This approach allows for backward compatibility and easier deployment of encryption on existing email servers without requiring a separate port for secure communication.