Replace it with a patch against the distribution configure.default,
which changes as little as possible so that folks who are accustomed to
Exim on other platforms will not be astonished.
Install the file as configure.default instead of configure.sample, since
it's as close as damnit to the default Exim configuration file.
The only arguably unnecessary deviation from the default is:
* Accept SMTP relay from the loopback IP address. Too many applications
require this, and the window of abuse is arguably negligible.
