We need more clarification to help you..
If your Name Servers point to Godaddy and your A records point to Rackspace and you purchased the email hosting on godaddy (which it sounds like you did to set up forwarders) then you most likely have the MX records set to something like smtp.secureserver.net (godaddy's mail servers), which just sounds like a complete mess.
Now most people will typically point the NS to Rackspace, then they will manage the DNS on rackspace and have the email hosted on rackspace and then use fowarders in that email system to whatever address you want. If this is your setup, then you will need to set up MX records on rackspace to point to rackspace mail servers, or point them back to godaddy to use their email servers.
Personally, I would just use Google Apps to host the email, and follow their instructions.
To get a better understanding how MX records work, here's some homework for you to go over.
MX Records Video