:allow
This will allow the specified IP range to make a connection

:deny
This will deny the specified IP range to make a connection

RELAYCLIENT=""
When set with :allow, this will accept relay messages from the specified IP
range

RBLSMTPD=""
When set with :allow or :deny, this will instruct smtpd to skip RBL checks for
the specified IP range

RBLSMTPD="my temp error message"
When set, this will skip RBL lookups but return "my temp error messsage" as a
4xx temp error for the specified IP range

RBLSMTPD="-my perm error message"
When set, this will skip RBL lookups and return "my perm error message" as a
5xx perm error for the specified IP range
Special thanks to Nick Holder