ra-retrieve: 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/ra-retrieve - from package: remembrance-agent

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

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