Is this an SPS Area or a WSS site? If it's an Area, then here's an example:

TopologyManager topologyManager = new TopologyManager();
Uri uri = new Uri("http://MyPortal");
PortalSiteCollection sites = topologyManager.PortalSites;
PortalContext portalContext = PortalApplication.GetContext(sites[uri]);
Guid homeGuid = AreaManager.GetSystemAreaGuid(portalContext, SystemArea.Home);
Area homeArea = AreaManager.GetArea(portalContext, homeGuid);
string emailAddress = homeArea.OwnerEmail;

If this is a WSS site:

SPWeb mySite = SPControl.GetContextWeb(Context);
string emailAddress = mySite.Author.Email;