coolmail: 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/coolmail - from package: coolmail

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

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