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Re: [ietf-smtp] fall back to clear text if TLS fails (was: draft-fenton-smtp-require-tls-00.txt)

2016-01-12 08:20:46
! 1.  Introduction
! ...
!    messages.  In this application, TLS is used only upon mutual
!    agreement (successful negotiation) between the client and server; if
!    this is not possible, the message is sent unencrypted.  Furthermore,

That's not the case for all MTAs. sendmail only recently introduced
an option to allow this:

        To automatically handle TLS interoperability problems for outgoing
                mail, sendmail can now immediately try a connection again
                without STARTTLS after a TLS handshake failure.

This was triggered due to the decision of OpenSSL to enforce some
policy in the library without a simple option to override that and
the resulting delivery problems...

Before that, mails would get stuck in the queue and hopefully get
the attention of a postmaster to fix the interoperability problem.

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