postconf: 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/postconf - from package: postfix

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

On Debian possible default full paths are:

/usr/sbin/postconf - from package: postfix

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

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