mailsnarf: 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/mailsnarf - from package: dsniff

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

On Debian possible default full paths are:

/usr/sbin/mailsnarf - from package: dsniff

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

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