Does LDIF routing apply to both outbound and inbound mail routing, overriding the MX record set in DNS?

Issue

Does LDIF routing apply to both outbound and inbound mail routing, overriding the MX record set in DNS?

For example, I have set up a VPN with a business partner, whose normal DNS has an MX record for the rest of the Internet that points to its public mail relay. My IP router has a static route that goes to the private relay. We want the mail we send each other to only go through our VPN to a private relay. Can I create an LDIF record for my partner's domain that has a mailhost value of the private relay, route mail through the VPN, and bypass the MX record for the public relay?

Solution

Yes. Domain routes in LDIF and LDAP are used to override MX resource records in DNS for both inbound and outbound mail routing.