inject: 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/inject - 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/inject - from package: mailman

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

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