How can I remove Sendmail from my system? I've built Exim and run make install, but it still doesn't seem to be fully operational.

If you are running FreeBSD, see `FAQ/FreeBSD/Q9201`_. Otherwise, you need to arrange that whichever of the paths /usr/sbin/sendmail or /usr/lib/sendmail exists on your system is changed to refer to Exim. For example, you could use these commands (as root):

mv /usr/sbin/sendmail /usr/sbin/sendmail.original
chmod u-s /usr/sbin/sendmail.original
ln -s /path/to/exim /usr/sbin/sendmail

The second command removes the setuid privilege from the old MTA, as a general safety precaution. In the third command, substitute the actual path to the Exim binary for /path/to/exim.