newbie - MX at nonstandard port setup in BIND

[Pedro Zorzenon Neto]

Hi all,

  I have a mail server that I want to receive mail.
  As my ISP policy is not let me receive incoming conections on port 25, I set up my mail server in a non standard port.
  Now comes the question:
  How do I specify in the DNS server (BIND 8.2.3) that a MX is in a non standard port?

   Thanks
   Pedro