virt_mail: 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/virt_mail - from package: virtuoso-opensource-6.1-bin

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

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