chewmail: 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 Debian possible default full paths are:

/usr/bin/chewmail - from package: chewmail

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

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