cancelmsg: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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/cancelmsg - from package: courier-mta

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