Optional list of DNS white/blacklist domains (see postscreen_dnsbl_sites parameter).
+`dnsbl_threshold`: `<integer> (0 - N)` ('default =' `1`)::
+
+The inclusive lower bound for blocking a remote SMTP client, based on its combined DNSBL score (see postscreen_dnsbl_threshold parameter).
+
`dwarning`: `<integer> (0 - N)` ('default =' `4`)::
SMTP delay warning time (in hours).
When set, all outgoing mails are deliverd to the specified smarthost.
+`smarthostport`: `<integer> (1 - 65535)` ('default =' `25`)::
+
+SMTP port number for smarthost.
+
`spf`: `<boolean>` ('default =' `1`)::
Use Sender Policy Framework.