Exchange can send mail, but not receive.

I am able to send email but not receive it. When I go to www.checkdns.net and do a test for my domain crestpsi.com. It says email is working fine. But when I open up users Outlook it doesnt receive mail and I get delivery messegaes returned after a couple of hours if I try to send these internal users email.

It was all working fine when I had my ISP do the DNS. Now I am doing it and it seems like it is fine, from the tests.

What should I look at for the problems?