Fellow monk, I'm afraid you simply are not clear enough. Where does the IP address show? In the email, at the client side? In a Recieved-line? In the browser when the mail is sent?

If the IPaddress is shown in the email at the From: or To: line, it's added by your local mailserver, because one of the email adresses were not complete, ie. <user> instead of <user@domain.cc>, the @ is vital here. Your local mailserver then adds it's official name. However, it may be not know it's officiall name, and then adds it's IPaddress as domain. You can send emails directly to IPaddresses, so they are valid on the right side of an @.

If your IPaddress show up on a Recieved: -line, I'm sorry, but that's how it's supposed to be. It's added by the next mailserver, indicating where it got the mail from, you can't change it.

If the browser shows the IP address when you have sent the mail, it's because you print it somewhere in your script.

Try specifying more accurately where it's showing the IPaddress in question and we'll see if we can help you.