Sven Reis

I would love that fix for setting `smtp_tls_security_level`, as transport security is turned off by default. It's neccessary to enable it via `smtp_tls_security_level = may` of higher, as described [here](https://www.claudiokuenzler.com/blog/275/howto-postfix-force-smtp-send-mail-with-tls-encryption-encrypted-starttls).

Better, there should be a parameter, instead of hard-coding `mtp_tls_security_level` to `encrypt`. A general solution would be setting `postconf -e key:value` pairs as in PR #40