Unfortunately, TFS doesn't have anything built out of the box for this to be done without recipient intervention. Richard Ev comment can work, but is not really sustainable. Each person needs to create this or you need to do it for them and continue doing it for all new team members.
Instead, you're better off creating an Event Subscriber. Here's a very helpful post http://www.codeproject.com/Articles/110292/Team-Foundation-Server-2010-Event-Handling-with-Su.
You'll want to use the IIdentityManagementService to retrieve the corresponding users' email. An example:
using (var projectCollection = TfsTeamProjectCollectionFactory.GetTeamProjectCollection(collectionUri, new UICredentialsProvider()))
{
var gss = projectCollection.GetService<IGroupSecurityService>();
var ims = projectCollection.GetService<IIdentityManagementService>();
var validUsersId = ims.ReadIdentity(IdentitySearchFactor.AccountName, "Team Foundation Valid Users", MembershipQuery.Expanded, ReadIdentityOptions.IncludeReadFromSource);
var validUsers = gss.ReadIdentities(SearchFactor.Sid, validUsersId.Members.Select(x => x.Identifier).ToArray(), QueryMembership.None);
foreach (var member in validUsers)
{
Console.WriteLine("{0}: {1}", member.AccountName, member.MailAddress);
}
}