Please visit the 'domain' settings page of your admin panel under the "Settings" top menu. Relevant mail server details will be posted there.
You can enter the mail server as shown in your admin, or your own mail.yourdomainname. Some ISP's such as Optus, iinet or Telstra provide dynamic IP addresses for residential accounts, in this case you can call them and ask about the settings for using their outgoing mail server. Otherwise you can host your domain and email on an external server and simply leave the "add to dns" box unchecked from the domain settings page. Doing this will allow you to point your domain to your store, but run your email externally to prevent any SPF problems.
