After all Routing Table records are applied, the Router checks if the domain name is actually an IP address. If the IP-address domain name is not enclosed into the square brackets, the Router encloses it: firstname.lastname@example.org is converted into email@example.com. This allows you to specify Routing Table records for IP addresses assuming that the address is always enclosed into square brackets.
For IP addresses enclosed in square brackets, the Router checks if the IP address is assigned to one of this Server Domains. If a Domain is found, the IP address is substituted with that Domain name. If the IP address is the IP address of the Server Main Domain, an empty string is placed into the domain name part, and the Router makes the next iteration after parsing the local name part of the address.
If an IP address is not assigned to a local Domain, the Router processes the [10.34.45.67] domain name as the 10.34.45.67.default_port._via name: the Router sends the address to the SIP or SMTP module, cutting off the domain part and using it as the host name to relay to.