Changed MX now can’t get mail

Up until Friday, we had pop dial up internet. I was using the exchange pop connector (through Small Business Server) to get me email. Friday we got dedicated cable Internet and now want our email forwarded to our exhange server form the ISP. I had the ISP add our IP address to their MX record but no mail is coming to our exchange server. I;ve sent several messages from outside and they do not arrive at the exchange server nor to they bounce back. I setup a receipt request on one and got a “message delayed” email. I’m trying to figure out where my problem is. Does anyone have a checklist to go through so I can make sure my exchange server is setup right? Any info will help. Thanks