Index: app/controllers/users_controller.rb
===================================================================
--- app/controllers/users_controller.rb	(revision 2940)
+++ app/controllers/users_controller.rb	(working copy)
@@ -39,12 +39,16 @@
         begin
           UserMailer.deliver_signup(@user, request.host_with_port, params[:to])
         rescue Net::SMTPFatalError => e
+          smtp_error(e)
           flash[:notice] = "A permanent error occured while sending the signup message to '{email}'. Please check the e-mail address."[:signup_permanent_error_message, @user.email]
           redirect_to :action => "new"
+          return
         rescue Net::SMTPServerBusy, Net::SMTPUnknownError, \
           Net::SMTPSyntaxError, TimeoutError => e
+          smtp_error(e)
           flash[:notice] = "The signup message cannot be sent to '{email}' at this moment. Please, try again later."[:signup_cannot_sent_message, @user.email]
           redirect_to :action => "new"
+          return
         end
         flash[:notice] = params[:email] ? "A temporary login email has been sent to '{email}'."[:temporary_login_message, @user.email] : "An account activation email has been sent to '{email}'."[:account_activation_message, @user.email]
         redirect_to CGI.unescape(login_path)
@@ -103,4 +107,8 @@
     def find_user
       @user = params[:id] ? User.find_by_id(params[:id]) : current_user
     end
+    
+    def smtp_error(error)
+      logger.error("Error sending email to #{@user.email}: #{error.class.name} '#{error}'\n#{error.backtrace*"\n"}")   
+    end
 end
Index: test/functional/users_controller_test.rb
===================================================================
--- test/functional/users_controller_test.rb	(revision 2940)
+++ test/functional/users_controller_test.rb	(working copy)
@@ -15,7 +15,28 @@
     @controller = UsersController.new
     @request    = ActionController::TestRequest.new
     @response   = ActionController::TestResponse.new
+    
+    UserMailer.class_eval do
+      unless method_defined? :signup_response
+        def signup_with_failure(user, domain, redirect_path, sent_at = Time.now)
+          case signup_response
+          when :fatal
+            raise Net::SMTPFatalError.new('error!')
+          when :server_busy
+            raise Net::SMTPServerBusy.new('error!')
+          else
+            signup_without_failure(user, domain, redirect_path, sent_at)
+          end
+        end
+        alias_method_chain :signup, :failure
+        cattr_accessor :signup_response
+      end
+    end
   end
+  
+  def teardown
+    UserMailer.signup_response = :default
+  end
 
   def test_should_get_index
     get :index
@@ -261,4 +282,16 @@
     assert users(:sam).reload.activated?
     assert_redirected_to home_path
   end
+  
+  def test_should_not_bomb_on_permanent_smtp_errors
+    UserMailer.signup_response = :fatal
+    post :create, :user => { :login => 'nico', :email => 'nico@email.com', :password => 'fooey', :password_confirmation => 'fooey' }
+    assert_redirected_to :controller => 'users', :action => 'new'
+  end
+  
+  def test_should_not_bomb_on_temporary_smtp_errors
+    UserMailer.signup_response = :server_busy
+    post :create, :user => { :login => 'nico', :email => 'nico@email.com', :password => 'fooey', :password_confirmation => 'fooey' }
+    assert_redirected_to :controller => 'users', :action => 'new'
+  end
 end
Index: test/fixtures/users.yml
===================================================================
--- test/fixtures/users.yml	(revision 2940)
+++ test/fixtures/users.yml	(working copy)
@@ -22,7 +22,7 @@
   last_seen_at: <%= 4.minutes.ago.to_s :db %>
   activated: true
   login_key: 8305f94ab2b92f99137abbc235ee28e5a
-  login_key_expires_at: <%= Time.now.utc + 1.week %>
+  login_key_expires_at: <%= (Time.now.utc + 1.week).to_s :db %>
 joe:
   id: 3
   login: joe