What Is SSL/TLS?
SSL (Secure Sockets Layer) and TLS (Transport Layer Security) are cryptographic protocols that encrypt data transmitted between clients and servers. TLS is the modern successor to SSL and is used to secure web traffic (HTTPS), email transmission, and other internet communications.
How SSL/TLS Works
When a client connects to a server over TLS, they perform a "handshake" to establish a secure connection. The server presents its certificate, the client verifies it against trusted Certificate Authorities (CAs), and both sides negotiate encryption parameters. Once the handshake completes, all data is encrypted in transit.
TLS 1.3, the latest version, streamlines the handshake to a single round-trip, improving both security and performance compared to older versions.
SSL/TLS and Email
TLS is also used to encrypt email in transit between mail servers. When your mail server sends an email, it can negotiate a TLS connection with the receiving server using STARTTLS. This prevents eavesdropping on the email content during transmission. However, without protocols like MTA-STS or DANE, this encryption is "opportunistic" — it can be downgraded by an attacker.
SSL vs TLS
SSL is the older protocol (SSL 2.0 and 3.0) and is now deprecated due to known vulnerabilities. TLS (1.0, 1.1, 1.2, 1.3) replaced SSL with stronger encryption and improved security. Today, only TLS 1.2 and 1.3 are considered secure. The term "SSL certificate" persists in common usage, but the certificates used today actually enable TLS connections.
Frequently Asked Questions
What is the difference between SSL and TLS?
SSL is the deprecated predecessor to TLS. TLS is the modern, secure version. When people say "SSL certificate" today, they almost always mean a certificate used with TLS. The latest version is TLS 1.3.
How does TLS protect email?
TLS encrypts the connection between mail servers during email transmission, preventing eavesdropping and tampering. MTA-STS and DANE can enforce TLS to prevent downgrade attacks.
How do I check if my SSL/TLS certificate is valid?
Use an SSL checker tool to verify your certificate's validity, expiration date, certificate chain, and protocol support. Email Armory offers a free SSL Checker for comprehensive certificate analysis.