How to change MX records

I have a domain which is using your free hosting service. I have a current gmail accout so I did not submit the google apps. service form DreamHost.

Now I cannot set my email forward setting from my original domain register supplier, and it show “validating MX records”. Because I set the nameservers to NS1.DREAMHOST.COM, NS2.DREAMHOST.COM and NS3.DREAMHOST.COM.

I want to solve this problem. Could you help and what can I do?