To replace smtpd with exim, install a new mailer.conf using the
following command:

    /usr/local/sbin/exim-enable

If you want to restore smtpd, this is done using the following
command:

    /usr/local/sbin/exim-disable

Note, SPA (NTLM) authentication has been disabled in the Exim 4.96.1 package.
It is also suggested to avoid Exim's SPF support as it uses libspf2 which may
still have unfixed serious vulnerabilites.
