Configure Exchange 2003 using local DNS and DynDNS

Greetings,

I’ve been trying to configure my exchange server for the last couple days but I’m running out of luck. Here’s my set up: DynDNS custom DNS account. I have my MX records on DynDNS.

@mycompany.com 10 mail.mycompany.com (those were just the text boxes to fill in the dyndns interface.

I can send internal email to users but I cannot accept outside email nor receive it. I understand that my ISP could block my outgoing on port 25 and I’ll have to deal with that later . could my local DNS cause an issue with my Custom DNS that’s hosted by DynDNS? Thank you