I was trying to setup Thunderbird. However when it came to specifying the outgoing server, Thunderbird said it would use my existing Earthlink outgoing server instead of yours. I tried to change this but it will not let me.
It is really not a problem to use earthlink for your outgoing. In fact many ISP’s (including earthlink) require you to use their outgoing SMTP. They firewall out external SMTP (port 25) to control all mail that leaves their network.
As long as your incoming POP3 is set to your domain with us it will work fine.