kmailcvt: 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/kmailcvt - from package: kdepim

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

On Debian possible default full paths are:

/usr/bin/kmailcvt - from package: kmail

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

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