exinext: 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/sbin/exinext - from package: exim

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

On Debian possible default full paths are:

/usr/sbin/exinext - from package: exim4-base

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

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