in.comsat: 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/sbin/in.comsat - from package: biff

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

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