Several software packages (like dcron) rely on /usr/lib/sendmail being a symlink to /usr/sbin/sendmail. While ssmtp provides this link, msmtp doesn't.
+*msmtp-1.4.24-r1 (22 Aug 2011) + + 22 Aug 2011; Eray Aslan <eras@gentoo.org> +msmtp-1.4.24-r1.ebuild: + add /usr/lib/sendmail symlink - bug #380209 +