/usr/bin/mailq
/usr/bin/mailq.opensmtpd
/usr/bin/newaliases
/usr/bin/newaliases.opensmtpd
/usr/sbin/makemap
/usr/sbin/makemap.opensmtpd
/usr/sbin/sendmail
/usr/sbin/sendmail.opensmtpd
/usr/sbin/smtpctl
/usr/sbin/smtpd
You may install this package on CentOS with
yum
install opensmtpd