TCP Mail

Port 465 (SMTPS)

Learn about port 465 (SMTPS) - security risks, vulnerabilities, and common uses. Find devices with port 465 open.

Quick Info

Port Number

465

Protocol

TCP

Service

SMTPS

IANA Name

SMTPS

Service Description

Port 465 (TCP) was initially designated for SMTPS (Simple Mail Transfer Protocol Secure), intended to provide implicit TLS/SSL encryption for SMTP connections right from the start. In this approach, the client immediately initiates a TLS/SSL handshake after establishing the TCP connection, unlike the STARTTLS mechanism on port 587 which upgrades an unencrypted connection to an encrypted one. While port 465 saw early adoption, it was officially deprecated by RFC 2487 in favor of STARTTLS. However, many older systems and some modern implementations still offer or require SMTPS on port 465, particularly for legacy compatibility or specific security configurations. Technically, when a client connects to a server on port 465, the server immediately presents its TLS certificate. The client then verifies the certificate and establishes an encrypted channel. Once the encrypted channel is established, standard SMTP commands are exchanged within the secure tunnel to send email. The initial TLS handshake is the key differentiator from port 587 using STARTTLS.

## Firewall Recommendations

Blocking port 465 is generally recommended if your organization is not actively using SMTPS and has migrated to STARTTLS on port 587. If you must use SMTPS on port 465, ensure that the server and client are configured with strong TLS ciphers (TLS 1.2 or higher is highly recommended) and that the server's TLS certificate is valid and properly configured. Regularly update the SMTP server software to patch any known vulnerabilities. Implement intrusion detection and prevention systems to monitor traffic on port 465 for suspicious activity. Consider using client certificate authentication for added security.

Security Information

While SMTPS on port 465 encrypts the communication, it also presents potential security risks. Misconfiguration of the TLS/SSL settings, such as using weak ciphers or outdated protocols (SSLv3, TLS 1.0), can make the connection vulnerable to man-in-the-middle attacks and data interception. Furthermore, the implicit TLS approach can mask underlying SMTP vulnerabilities. Attackers might exploit unpatched SMTP server software through the encrypted channel. The fact that it's often a 'legacy' service means patching and security updates might be less frequent, increasing the risk. Attackers may target this port hoping to exploit older, less secure configurations or unpatched vulnerabilities in the underlying SMTP server.