There exist multiple issues with these options, for example they are not
introspectable, since the values are configured in the config part of the
module.
Also the keypair is always configured for both server and client usage,
which is really surprising. The postfix docs even advise against setting
up client certificates, if they aren't required. [1]
The replacements are the `smtpd_tls_chain_files` for server usage and
`smtp_tls_chain_files` for client usage, which are the prefered way to
configure keys and certificates since Postfix 3.4.0. [2]
[1] https://www.postfix.org/postconf.5.html#smtp_tls_cert_file
[2] https://www.postfix.org/postconf.5.html#smtpd_tls_cert_file
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