Merge branch '5786-dane' into 'develop'

Use DANE if TLSA records are present

Closes #5786

See merge request ispconfig/ispconfig3!1235

install/tpl/postfix_2-5.conf.master

@@ -11,3 +11,4 @@
 #{stress_adaptive} smtpd_soft_error_limit = ${stress?2}${stress:5}
 #{stress_adaptive} smtpd_timeout = ${stress?10}${stress:60}s
 
+smtpd_forbidden_commands = CONNECT,GET,POST,USER,PASS

install/tpl/postfix_3-0.conf.master

@@ -11,3 +11,6 @@
 #{stress_adaptive} smtpd_soft_error_limit = ${stress?{2}:{5}}
 #{stress_adaptive} smtpd_timeout = ${stress?{10}:{60}}s
 
+# validate DANE
+smtp_dns_support_level = dnssec
+smtp_tls_security_level = dane