http://blogs.technet.com/blairb/archive/2008/05/08/unable-to-send-e-mail-alerts-to-users-with-an-external-email-address.aspxThis one is short and sweet. My customer has federated partners so we use ADFS to allow these partners the ability to access and collaborate with our SharePoint portal. One of our amazing developers wrote code to create user profiles in the ADFS enableden-USCommunityServer 2.1 SP1 (Build: 61025.2)