r2e: 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/r2e - from package: rss2email

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

On Debian possible default full paths are:

/usr/bin/r2e - from package: rss2email

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

Error in other languages:
r2e: bevel nie gevind nie
r2e: comandă negăsită
r2e: comando não encontrado
r2e: commande introuvable
r2e: command not found
r2e: käsku ei ole
r2e: không tìm thấy lệnh
r2e: komanda nerasta
r2e: Kommando nicht gefunden.
r2e: kommandot finns inte
r2e: komut yok
r2e: nie znaleziono polecenia
r2e: níor aimsíodh an t-ordú
r2e: no se encontró la orden
r2e: no s'ha trobat l'ordre
r2e: opdracht niet gevonden
r2e: parancs nem található
r2e: perintah tidak ditemukan
r2e: príkaz nenájdený
r2e: příkaz nenalezen
r2e: команда не найдена
r2e: командата не е открита
r2e: 命令找不到
r2e: コマンドが見つかりません