Hi Chris,
Speak to your Domain host and have them point the primary MX record to your IP Address (Yes, yes, MX records cannot point to IP addresses - your Domain host must probably create a CNAME or something for this to work). If you don't have a static IP, create a DynDNS account to track your Dynamic IP and ask your Domain host to point the primary MX of your domain to the DynDNS domain name your created.
Kelvin