What this RFC defined
RFC 5246 defined TLS version 1.2, the Transport Layer Security protocol that encrypted the majority of internet traffic for over a decade. It introduced AEAD cipher suites, improved pseudorandom function definitions, and made several security improvements over TLS 1.1. TLS 1.2 was the dominant encryption protocol for email until TLS 1.3 became widely deployed.
Where you would have seen it in practice
The TLS 1.2 handshake seen in mail server logs (TLSv1.2, cipher ECDHE-RSA-AES256-GCM-SHA384) followed the protocol defined in RFC 5246. Most email servers configured between 2008 and 2020 defaulted to TLS 1.2. Many production mail servers still support TLS 1.2 for backward compatibility with older clients, though TLS 1.3 is now preferred for new connections.
How it connects to other RFCs
RFC 5246 obsoletes RFC 4346 (TLS 1.1) and is itself obsoleted by RFC 8446 (TLS 1.3). For email, it was referenced by RFC 3207 (STARTTLS for SMTP) and RFC 8314 (TLS for email submission). The cipher suite improvements in RFC 5246 informed the more radical redesign of TLS 1.3 in RFC 8446.
Current status
RFC 5246 was formally obsoleted by RFC 8446 (TLS 1.3) in 2018. TLS 1.0 and 1.1 have been deprecated; TLS 1.2 remains in wide use for backward compatibility but TLS 1.3 should be preferred for new deployments. Most major mail servers support both versions to handle older clients and servers in transit.
The TLS 1.2 protocol
RFC 5246 defined TLS 1.2 in August 2008 and was the dominant transport security protocol for HTTPS, SMTP STARTTLS, IMAPS, and countless other secure protocols from roughly 2010 through 2020. Compared to TLS 1.1, version 1.2 added SHA-256 as the default hash for signatures, introduced authenticated encryption (AEAD) cipher suites like AES-GCM, and cleaned up the handshake to remove several legacy dependencies on MD5 and SHA-1.
Cipher suite selection matters
The security of a TLS 1.2 connection depends heavily on which cipher suite the two endpoints negotiate. Modern recommendations are the ECDHE key exchange (forward secrecy) with AES-GCM or ChaCha20-Poly1305 encryption and SHA-256 or SHA-384 hashing. Older suites using RSA key exchange (no forward secrecy), CBC mode ciphers (vulnerable to padding oracle attacks), or SHA-1 (broken) should be disabled server-side. Every MTA (Postfix, Exim, Sendmail) exposes cipher configuration; getting it wrong means legitimate mail is encrypted with weak ciphers.
Superseded by TLS 1.3
RFC 8446 defined TLS 1.3 in August 2018 and is the current standard. TLS 1.3 removed all weak cipher suites, halved the handshake round trips, and provided better forward secrecy by default. Every major browser and mail client supports TLS 1.3 in 2026, and TLS 1.2 remains supported for backward compatibility. Downgrade protection in TLS 1.3 prevents active attackers from forcing endpoints back to TLS 1.2. Deployments should support both versions for compatibility with older peers.
About the Author
Alaa · LinkedIn
Email infrastructure specialist with 8+ years of hands-on experience in SMTP, deliverability, and email verification. I’ve configured and troubleshot mail systems across Postfix, Exchange, and cloud relays, managed IP reputation and warmup campaigns, and built verification pipelines processing millions of addresses. My work spans DNS authentication (SPF, DKIM, DMARC, BIMI), bounce handling, blocklist monitoring, and compliance frameworks including CAN-SPAM and GDPR. I write every article on SMTPedia to give email professionals, developers, and marketers the accurate, RFC-grounded reference they need.
About SMTPedia
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