Implemented SMTP submission proxy service.

Replace ssl_protocols config option with ssl_min_protocol Default to TLSv1.

ssl: deprecate no_compression in ssl_options Compression is now disabled by default.

doc: mention no_ticket in ssl config example

doc: remove obsolete ssl_dh_parameters_length from example config

ssl: change to more secure default ssl_cipher_list

ssl: add ssl_curve_list setting for selecting ECHDE curves

doc: add ssl_dh to example-config

ssl: fix reference to SSLv2 and disable SSLv3 This is driven by the fact that OpenSSL 1.1 does not know about SSLv2 at all and dovecot's defaults simply make OpenSSL error out with "Unknown protocol 'SSLv2'"[1]. So we change the defaults to refer to SSLv2 iff OpenSSL seems to know something about it. While at it, it's also a good idea to disable SSLv3 by default as well. [1] https://bugs.debian.org/844347 Signed-off-by: Apollon Oikonomopoulos <apoikos@debian.org>

example-config: Added ssl_options setting.

ssl-params: Added ssl_dh_parameters_length & removed ssl_parameters_regenerate setting. ssl_parameters_regenerate was based on some text from GNUTLS documentation a long time ago, but there's really not much point in doing it. Ideally we should also support "openssl dhparam" input files, but for now there's the ssl_dh_parameters_length setting that can be used to specify the wanted DH parameters length. If the current ssl-parameters.dat has a different length, it's regenerated. We should probably at some point support also built-in DH parameters which are returned while the ssl-params runs.

Added ssl_prefer_server_ciphers setting.

example-config: Added ssl_client_ca_file

example-config: Added ssl_client_ca_dir setting.

*-login: Added ssl_require_crl setting.

example-config: Added ssl_crypto_device.

Added ssl_protocols setting.

example-config: Added nn- prefix to *.conf files so the sort ordering makes more sense. This is especially important to get mail_plugins = $mail_plugins example working in protocol sections. --HG-- branch : HEAD