vboxmail: 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/bin/vboxmail - from package: isdn4k-utils

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

On Debian possible default full paths are:

/usr/sbin/vboxmail - from package: isdnvboxserver

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

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