Implementing Domino server

Hi guys,I’m new in Domino world; But i want to install a domino server on a local machine that will pull and push my organisation mail from our mail domamain host(which is hosted by another company outside my country).

I made an attempt to configure a server for this purpose but I can only send mails to any domain but can not get the replied mail to the server.

do i need any 3rd part software;

how would I edit my DNS to change the IP of my domain name to another Public IP?

pls help