snmail: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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/sbin/snmail - from package: sn

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