I think this is the default. If no routing information is found in LDAP it will route normally. (If SMTP routes are configured use those, if not do an MX lookup, if that fails use a A lookup, if that fails (after 4 days by default) bounce the mail home)
You don't have to use LDAP routing at all, you can use the SMTProutes when you have static delivery. There is no need to LDAP routing unless your company has many different backend systems for people in the same domain with there mail box on different physical servers.
We have configured the outside and inside Interface with official ipv6 adresses, set a default route on outside Interface to our router, we also have definied a rule , which also gets hits, to permit tcp from inside Interface to any6.
In Syslog I also se...