[Ach] Update postfix settings

[Albert Krewinkel]

New Postfix default settings might require reevaluation of some
parameters.  The recommendation currently is to leave the
`smtpd_tls_cipherlist` unchanged for maximum interoperability with other
servers.  The recommendation is now inconsistend across different
Postfix versions, as above parameter no longer defaults to `export` but
to `medium` in newer Postfix versions[1].  My preference would be to
follow the newer default and recommend the parameter to be set to
`medium`.  Same with `smtp_tls_cipherlist`.

Cheers,
/a

[1]: http://www.postfix.org/postconf.5.html#smtpd_tls_ciphers

-- 
Albert Krewinkel
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