Your boss is...less than optimally correct
...
You can't change the domain name but if he's worried about mail delivery via the Exchange component he doesn't need to be; even if the internal name is mycompany.local or somesuch, you can accept mail for another "real" domain name by setting the recipient policies for Exchange. Ours is an Exchange2K server, but the principle's still the same. If that's what's giving him fits, tell him not to worry.
And amen on the weekend part...