test.ss
#lang scheme
(require "main.ss")
(define (open-message path)
  (call-with-input-file path read-message))

(define (get-message-body message)
  (map mime-body (mime-body (mime-body message))))

(define files '("/Users/yinso/Documents/test.message.txt"
                "/Users/yinso/Documents/test.multipart.txt"
                "/Users/yinso/Documents/message-jpg-attachment.txt"
                "/Users/yinso/Documents/delivery-status-message.txt"
                ;; "/Users/yinso/Documents/message-jpg-attachment-error.txt"
                ;; this verifies error are returned from the filter thread and kill
                ;; the existing evaluation...
                ))

(map (compose get-message-body open-message) files)