DNS Mods required for dicussion list setup

I cannot change the nameservers to dreamhost on a domain I manage. The DNS is managed at godaddy. I want to configure discussion list on list.[mydomain].com . I have created an A record for list to point at my dreamhost server, but what else needs to be configured. I thought “list” had to be setup as a MX record, but when I do that I get a loopback error on message sent to the account. Any help on clarifying how I properly configure DNS for domain managed at another registrar but using discussion list functionality at Dreamhost would be appreciated.