E-mail encryption
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E-mail encryption refers to encryption, and often authentication, of e-mail messages. E-mail encryption can rely on public-key cryptography.
[edit] E-mail encryption protocols
Popular protocols for e-mail encryption include:
- S/MIME
- TLS
- OpenPGP
- Identity based encryption
- Mail sessions encryption
[edit] Mail sessions encryption
The STARTTLS SMTP extension is not 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 e-mails because the content of messages is revealed to, and can be tampered with by, involved 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 e-mail's contents are encrypted using another protocol.
STARTTLS is also an extension of IMAP4 and POP3, see RFC 4616.