code: def diff(self, mail_a, mail_b):
          
          return len(''.join(unified_diff(
              mail_a.body_lines, mail_b.body_lines,
              # Ignore difference in filename lenghts and timestamps.
              fromfile='a', tofile='b',
              fromfiledate='', tofiledate='',
              n=0, lineterm='\n')))
docs: Return difference in bytes between two mails' normalized body.
  
          TODO: rewrite the diff algorithm to not rely on naive unified diff
          result parsing.