PREUN

/bin/sh

if [ $1 = 0 ]; then
        update-alternatives --remove sendmail-command /usr/bin/msmtp
fi

POSTIN

/bin/sh

update-alternatives \
	--install /usr/sbin/sendmail sendmail-command /usr/bin/msmtp 5 \
	--slave /usr/lib/sendmail sendmail-command-in_libdir /usr/bin/msmtp