mailutil: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/mailutil - from package: uw-imap-utils

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/mailutil - from package: uw-mailutils

You may install the required package with command apt-get install {package}

Error in other languages:
mailutil: bevel nie gevind nie
mailutil: comandă negăsită
mailutil: comando não encontrado
mailutil: commande introuvable
mailutil: command not found
mailutil: käsku ei ole
mailutil: không tìm thấy lệnh
mailutil: komanda nerasta
mailutil: Kommando nicht gefunden.
mailutil: kommandot finns inte
mailutil: komut yok
mailutil: nie znaleziono polecenia
mailutil: níor aimsíodh an t-ordú
mailutil: no se encontró la orden
mailutil: no s'ha trobat l'ordre
mailutil: opdracht niet gevonden
mailutil: parancs nem található
mailutil: perintah tidak ditemukan
mailutil: príkaz nenájdený
mailutil: příkaz nenalezen
mailutil: команда не найдена
mailutil: командата не е открита
mailutil: 命令找不到
mailutil: コマンドが見つかりません