postcat: 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/sbin/postcat - from package: postfix

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

On Debian possible default full paths are:

/usr/sbin/postcat - from package: postfix

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

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