list_admins: 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/list_admins - 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/list_admins - from package: mailman
/usr/sbin/list_admins - from package: mailman

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

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