code: def mime(self):
  		
  		author = self.author
  		sender = self.sender
  		
  		if not author:
  			raise ValueError("You must specify an author.")
  
  		if not self.subject:
  			raise ValueError("You must specify a subject.")
  
  		if len(self.recipients) == 0:
  			raise ValueError("You must specify at least one recipient.")
  
  		if not self.plain:
  			raise ValueError("You must provide plain text content.")
  
  		# DISCUSS: Take the first author, or raise this error?
  		# if len(author) > 1 and len(sender) == 0:
  		#	 raise ValueError('If there are multiple authors of message, you must specify a sender!')
  
  		# if len(sender) > 1:
  		#	 raise ValueError('You must not specify more than one sender!')
  
  		if not self._dirty and self._processed:
  			return self._mime
  
  		self._processed = False
  
  		plain = MIMEText(self._callable(self.plain), 'plain', self.encoding)
  
  		rich = None
  		if self.rich:
  			rich = MIMEText(self._callable(self.rich), 'html', self.encoding)
  
  		message = self._mime_document(plain, rich)
  		headers = self._build_header_list(author, sender)
  		self._add_headers_to_message(message, headers)
  
  		self._mime = message
  		self._processed = True
  		self._dirty = False
  
  		return message
docs: Produce the final MIME message.