Possible workaround
As Russell stated, there is no default
way to change the behavior as we primarily want to route through NRPC when
possible. However, you can perform one of the following actions to
route internally using the internet address on a per user basis. There
is no global configuration to change the behavior.
1. Add @domain to the end of the
address. For example: john_doe@acme.com@acmedomain
2. Add the recipient's internet
address to the sender's personal address book, open the Location doc, and
set Recipient name lookup to Stop after first match.