Opportunistic TLS


Opportunistic TLS is a Opportunistic encryption concept for optimal use of encryption.

Currently implemented in as StartTLS and a few other protocols where the he sending server attempts to send a message encrypted, but if the receiving server will or can not accept encrypted messages then the mail is sent Plaintext. Not all of your messages are encrypted this way, but the important takeaway is that it is encrypted whenever possible and should be accepted by all ISPs/inbox providers.

Opportunistic TLS SMTP Submission, IMAP, POP, and ManageSieve clients#

RFC 7817 describes the Transport Layer Security (TLS) server identity verification procedure for SMTP Submission, IMAP, POP, and ManageSieve clients.


File Transfer Protocol (FTP) Securing FTP with TLS (RFC 4217) for negotiating TLS is the character string identified in {TLS-PARM}. This allows the client and server to negotiate TLS on the control connection without altering the protection of the data Channel.

More Information#

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