A0428 reads:
This is the same question as Q0402. The duplication is a bug in the FAQ.
Shouldn't that be Q0403 ?
Q0402: How do I configure Exim to send all messages to a central server?
Q0403: How do I configure Exim to send messages for unknown local users
to a central server?
--
Magically means "transparently doing something very complicated" -- Camel Book