Email encryption

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Email encryption refers to encryption, and often authentication, of email messages, to protect the content from being read by any but the intended recipients.

Email encryption can rely on public-key cryptography, in which users can each publish a public key that others can use to encrypt messages to them, while keeping secret a private key they can use to decrypt such messages or to digitally encrypt and sign messages they send.

Encryption protocols[edit]

Protocols for email encryption include:

Mail sessions encryption[edit]

The STARTTLS SMTP extension is a TLS (SSL) layer on top of the SMTP connection. While it protects traffic from being sniffed during transmission, it is technically not encryption of emails because the content of messages is revealed to, and can therefore be altered by, intermediate email relays. In other words, the encryption takes place between individual SMTP relays, not between the sender and the recipient. When both relays support STARTTLS, it may be used regardless of whether the email's contents are encrypted using another protocol.

STARTTLS is also an extension of IMAP4 and POP3, see RFC 4616.


The Signed and Encrypted Email Over The Internet demonstration has shown that organizations can collaborate effectively using secure email. Previous barriers to adoption were overcome, including the use of a PKI bridge to provide a scalable public key infrastructure (PKI) and the use of network security guards checking encrypted content passing in and out of corporate network boundaries to avoid encryption being used to hide malware introduction and information leakage.

See also[edit]