cvm-vmailmgr-udp: 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/cvm-vmailmgr-udp - from package: cvm

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

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