newlist: 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/lib/mailman/bin/newlist - from package: mailman

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

On Debian possible default full paths are:

/usr/lib/mailman/bin/newlist - from package: mailman
/usr/sbin/newlist - from package: mailman

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

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