user@server:~$ whereis sendmail
sendmail: /usr/sbin/sendmail /usr/lib/sendmail /usr/share/man/man8/sendmail.8.gz
user@server:~$ ls -la /usr/sbin/sendmail
lrwxrwxrwx 1 root root 5 avril  3  2018 /usr/sbin/sendmail -> ssmtp