resolved issue 244 and updated test

app/models/user.rb

@@ -30,7 +30,7 @@ class User < ActiveRecord::Base
   scope :not_in_project, lambda { |project|  where("id not in (:ids)", :ids => project.users.map(&:id) ) }
 
   def identifier
-    email.gsub "@", "_"
+    email.gsub /[@.]/, "_"
   end
 
   def is_admin?

spec/models/user_spec.rb

@@ -16,7 +16,7 @@ describe User do
 
   it "should return valid identifier" do
     user = User.new(:email => "test@mail.com")
-    user.identifier.should == "test_mail.com"
+    user.identifier.should == "test_mail_com"
   end
 
   it "should have authentication token" do