mailmanctl: 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/mailmanctl - 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/mailmanctl - from package: mailman

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

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