procmail: 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/procmail - from package: procmail

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

On Debian possible default full paths are:

/usr/bin/procmail - from package: procmail

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

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