Hello and welcome to LQ, hope you like it here.
You can perform those tasks with a Procmail recipe that selects the message by its subject ("* ^Subject:.*Reclamo") and pipe the message through OpenSSL in base64 mode, mmencode, metamail or equivalent to save the attachment to a temporary file. If your application handles unconverted Mcrsft Excel then you could just fill a variable with the tempfile name and "| sh /the/application $variable". Want to tinker with it yourself (10 pts) or do you want the recipe?