newaliases.postfix: command not found

Have You tried accessing the binary with the full path?

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

[root@server ~]# echo $PATH

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/newaliases.postfix - from package: postfix

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