postalias: 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/postalias - from package: postfix

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

On Debian possible default full paths are:

/usr/sbin/postalias - from package: postfix

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

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