: start( address, port = 110, account, password )
: start( address, port = 110, account, password ) {|pop| .... }
    address  port ֥ݡȤ³ account ѥ
    password  POP 󤷤ޤ port  nil Ϥ
    POP3 Υǥեȥݡ(110)Ȥޤ

      Net::POP3.start( addr, port, account, password ) {|pop|
        pop.each_mail do |m|
          file.write m.pop
          m.delete
        end
      }

