diff --git a/app/controllers/users_controller.rb b/app/controllers/users_controller.rb
--- a/app/controllers/users_controller.rb
+++ b/app/controllers/users_controller.rb
@@ -1,8 +1,9 @@
-require 'pony'
+require 'tmail'
+require 'net/smtp'
 
 class UsersController < ApplicationController
 
-  before_filter :authenticate, :except => [:new, :register]
+  before_filter :authenticate, :except => [:new, :register, :confirm]
 
   verify :method => :post, :only => [:chg_passwd],
          :redirect_to => { :action => :index }
@@ -40,17 +41,76 @@
     @user.password_confirmation = @user.password = User.random_password
     @user.activated = false
     if (@user.valid?) and (@user.save)
-      send_confirmation_email(@user)
-      render :action => 'new_splash', :layout => 'empty'
+      if send_confirmation_email(@user)
+        render :action => 'new_splash', :layout => 'empty'
+      else
+        render :action => 'email_error', :layout => 'empty'
+      end
     else
       @user.errors.add_to_base("Email cannot be blank") if @user.email==''
       render :action => 'new', :layout => 'empty'
     end
   end
 
+  def confirm
+    login = params[:login]
+    key = params[:activation]
+    user = User.find_by_login(login)
+    if (user) and (user.verify_activation_key(key))
+      if user.valid?  # check uniquenss of email
+        user.activated = true
+        user.save
+        @result = :successful
+      else
+        @result = :email_used
+      end
+    else
+      @result = :failed
+    end
+    render :action => 'confirm', :layout => 'empty'
+  end
+
   protected
 
   def send_confirmation_email(user)
+    contest_name = Configuration['contest.name']
+    activation_url = url_for(:action => 'confirm', 
+                             :login => user.login, 
+                             :activation => user.activation_key)
+    home_url = url_for(:controller => 'main', :action => 'index')
+    mail = TMail::Mail.new
+    mail.to = user.email
+    mail.from = Configuration['system.online_registration.from']
+    mail.subject = "[#{contest_name}] Confirmation"
+    mail.body = <<-EOF
+Hello #{user.full_name},
+
+You have registered for #{contest_name} (#{home_url}).  
+
+Your login is: #{user.login}
+Your password is: #{user.password}
+
+Please follow the link:
+#{activation_url}
+to activate your user account.
+
+If you did not register, please ignore this e-mail.
+
+Thanks!
+EOF
+
+    smtp_server = Configuration['system.online_registration.smtp']
+
+    begin
+      Net::SMTP.start(smtp_server) do |smtp|
+        smtp.send_message(mail.to_s, mail.from, mail.to)
+      end
+      result = true
+    rescue
+      result = false
+    end
+
+    return result
   end
   
 end
diff --git a/app/models/configuration.rb b/app/models/configuration.rb
--- a/app/models/configuration.rb
+++ b/app/models/configuration.rb
@@ -36,6 +36,10 @@
     @@configurations = nil
   end
 
+  def self.enable_caching
+    @@cache = true
+  end
+
   #
   # View decision
   #
diff --git a/app/models/user.rb b/app/models/user.rb
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -19,7 +19,7 @@
   belongs_to :site
   belongs_to :country
 
-  named_scope :activated, :conditions => {:activated => true}
+  named_scope :activated_users, :conditions => {:activated => true}
 
   validates_presence_of :login
   validates_uniqueness_of :login
@@ -36,6 +36,7 @@
   validates_format_of :email, :with => /\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\Z/i, :allow_blank => true
 
   validate :uniqueness_of_email_from_activated_users
+  validate :enough_time_interval_between_same_email_registrations
 
   attr_accessor :password
 
@@ -87,6 +88,9 @@
   end
 
   def activation_key
+    if self.hashed_password==nil
+      encrypt_new_password
+    end
     Digest::SHA1.hexdigest(self.hashed_password)[0..7]
   end
 
@@ -117,8 +121,18 @@
     end
 
     def uniqueness_of_email_from_activated_users
-      if User.activated.find_by_email(self.email)!=nil
+      user = User.activated_users.find_by_email(self.email)
+      if user and (user.login != self.login)
         self.errors.add_to_base("Email has already been taken")
       end
     end
+    
+    def enough_time_interval_between_same_email_registrations
+      open_user = User.find_by_email(self.email,
+                                     :order => 'created_at DESC')
+      if open_user and open_user.created_at and 
+          (open_user.created_at > Time.now.gmtime - 5.minutes)
+        self.errors.add_to_base("There are already unactivated registrations with this e-mail address (please wait for 5 minutes)")
+      end
+    end
 end
diff --git a/app/views/users/confirm.html.haml b/app/views/users/confirm.html.haml
new file mode 100644
--- /dev/null
+++ b/app/views/users/confirm.html.haml
@@ -0,0 +1,15 @@
+- if @result == :successful
+  %h1 User activated
+  Your account has been activated.
+  %br/
+  Please go ahead to
+  = link_to 'login.', :controller => 'main', :action => 'login'
+- else
+  %h1 Activation failed
+  - if @result == :email_used
+    A user with this E-mail exists.
+  - else 
+    Your activation code is invalid.  Please check again.
+  %br/
+  Get back to
+  = link_to 'home.', :controller => 'main', :action => 'login'
diff --git a/app/views/users/email_error.html.haml b/app/views/users/email_error.html.haml
new file mode 100644
--- /dev/null
+++ b/app/views/users/email_error.html.haml
@@ -0,0 +1,9 @@
+%h1 Errors in sending registration confirmation
+
+.errorExplanation
+  %h2 
+    Your user account has been created, but the system cannot send you the
+    confirmation e-mail.
+
+  Maybe there's a problem in the configuration.  Please report the
+  admin.  Thank you!
diff --git a/config/environment.rb.SAMPLE b/config/environment.rb.SAMPLE
--- a/config/environment.rb.SAMPLE
+++ b/config/environment.rb.SAMPLE
@@ -50,7 +50,7 @@
   # This is for rspec
   config.gem "rspec-rails", :lib => "spec" 
   config.gem "haml"
-  config.gem "pony"
+  config.gem "tmail"
   #config.gem "BlueCloth", :lig => "bluecloth"
 end
 
@@ -72,3 +72,6 @@
 # These are where inputs and outputs of test requests are stored
 TEST_REQUEST_INPUT_FILE_DIR = RAILS_ROOT + '/data/test_request/input'
 TEST_REQUEST_OUTPUT_FILE_DIR = RAILS_ROOT + '/data/test_request/output'
+
+# Uncomment so that configuration is read only once when the server is loaded
+# Configuration.enable_caching
diff --git a/db/migrate/20081205172258_add_emailing_info_on_config_option.rb b/db/migrate/20081205172258_add_emailing_info_on_config_option.rb
new file mode 100644
--- /dev/null
+++ b/db/migrate/20081205172258_add_emailing_info_on_config_option.rb
@@ -0,0 +1,18 @@
+class AddEmailingInfoOnConfigOption < ActiveRecord::Migration
+  def self.up
+    # If Configuration['system.online_registration'] is true, the
+    # system allows online registration, and will use these
+    # information for sending confirmation emails.
+    Configuration.create(:key => 'system.online_registration.smtp',
+                         :value_type => 'string',
+                         :value => 'smtp.somehost.com')
+    Configuration.create(:key => 'system.online_registration.from',
+                         :value_type => 'string',
+                         :value => 'your.email@address')
+  end
+
+  def self.down
+    Configuration.find_by_key("system.online_registration.smtp").destroy
+    Configuration.find_by_key("system.online_registration.from").destroy
+  end
+end
diff --git a/db/migrate/20081210021333_add_timestamps_to_users.rb b/db/migrate/20081210021333_add_timestamps_to_users.rb
new file mode 100644
--- /dev/null
+++ b/db/migrate/20081210021333_add_timestamps_to_users.rb
@@ -0,0 +1,9 @@
+class AddTimestampsToUsers < ActiveRecord::Migration
+  def self.up
+    add_timestamps :users
+  end
+
+  def self.down
+    remove_timestamps :users
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -9,7 +9,7 @@
 #
 # It's strongly recommended to check this file into your version control system.
 
-ActiveRecord::Schema.define(:version => 20081204122651) do
+ActiveRecord::Schema.define(:version => 20081210021333) do
 
   create_table "announcements", :force => true do |t|
     t.string   "author"
@@ -174,15 +174,17 @@
   add_index "test_requests", ["user_id", "problem_id"], :name => "index_test_requests_on_user_id_and_problem_id"
 
   create_table "users", :force => true do |t|
-    t.string  "login",           :limit => 10
-    t.string  "full_name"
-    t.string  "hashed_password"
-    t.string  "salt",            :limit => 5
-    t.string  "alias"
-    t.string  "email"
-    t.integer "site_id"
-    t.integer "country_id"
-    t.boolean "activated",                     :default => false
+    t.string   "login",           :limit => 10
+    t.string   "full_name"
+    t.string   "hashed_password"
+    t.string   "salt",            :limit => 5
+    t.string   "alias"
+    t.string   "email"
+    t.integer  "site_id"
+    t.integer  "country_id"
+    t.boolean  "activated",                     :default => false
+    t.datetime "created_at"
+    t.datetime "updated_at"
   end
 
   add_index "users", ["login"], :name => "index_users_on_login", :unique => true
diff --git a/public/stylesheets/application.css b/public/stylesheets/application.css
--- a/public/stylesheets/application.css
+++ b/public/stylesheets/application.css
@@ -82,6 +82,14 @@
     font-size: 13px;
 }
 
+div.errorExplanation {
+    border: 1px dashed black;
+    color: black;
+    padding: 5px;
+    margin-bottom: 5px;
+    background-color: white;
+}
+
 /*******************************
  [Settings]
 ********************************/
diff --git a/script/spec b/script/spec
--- a/script/spec
+++ b/script/spec
@@ -1,4 +1,5 @@
 #!/usr/bin/env ruby
 $LOAD_PATH.unshift(File.expand_path(File.dirname(__FILE__) + "/../vendor/plugins/rspec/lib"))
+require 'rubygems'
 require 'spec'
 exit ::Spec::Runner::CommandLine.run(::Spec::Runner::OptionParser.parse(ARGV, STDERR, STDOUT))
diff --git a/spec/controllers/main_controller_spec.rb b/spec/controllers/main_controller_spec.rb
--- a/spec/controllers/main_controller_spec.rb
+++ b/spec/controllers/main_controller_spec.rb
@@ -4,7 +4,7 @@
 describe MainController do
 
   before(:each) do
-    @problem = mock(Problem, :name => 'test')
+    @problem = mock(Problem, :name => 'test', :output_only => false)
     @language = mock(Language, :name => 'cpp', :ext => 'cpp')
     @submission = mock(Submission,
                        :id => 1,
@@ -14,6 +14,7 @@
                        :source => 'sample source',
                        :compiler_message => 'none')
     @user = mock(User, :id => 1, :login => 'john')
+    @another_user = mock(User, :id => 2, :login => 'mary')
   end
 
   it "should redirect user to login page when unlogged-in user try to access main/list" do
@@ -23,18 +24,21 @@
 
   it "should let user sees her own source" do
     Submission.should_receive(:find).with(@submission.id.to_s).and_return(@submission)
+    User.should_receive(:find).with(1).and_return(@user)
     get 'source', {:id => @submission.id}, {:user_id => 1}
     response.should be_success
   end
 
   it "should let user sees her own compiler message" do
     Submission.should_receive(:find).with(@submission.id.to_s).and_return(@submission)
+    User.should_receive(:find).with(1).and_return(@user)
     get 'compiler_msg', {:id => @submission.id}, {:user_id => 1}
     response.should be_success
   end
 
   it "should not let user sees other user's source" do
     Submission.should_receive(:find).with(@submission.id.to_s).and_return(@submission)
+    User.should_receive(:find).with(2).and_return(@another_user)
     get 'source', {:id => @submission.id}, {:user_id => 2}
     flash[:notice].should =~ /[Ee]rror/ 
     response.should redirect_to(:action => 'list')
@@ -42,6 +46,7 @@
 
   it "should not let user sees other user's compiler message" do
     Submission.should_receive(:find).with(@submission.id.to_s).and_return(@submission)
+    User.should_receive(:find).with(2).and_return(@another_user)
     get 'compiler_msg', {:id => @submission.id}, {:user_id => 2}
     flash[:notice].should =~ /[Ee]rror/ 
     response.should redirect_to(:action => 'list')
diff --git a/spec/controllers/test_controller_spec.rb b/spec/controllers/test_controller_spec.rb
--- a/spec/controllers/test_controller_spec.rb
+++ b/spec/controllers/test_controller_spec.rb
@@ -7,7 +7,7 @@
     @john = mock(User, :id => "1", :login => 'john')
     @john_result = mock(TestRequest, :id => "1", :user_id => @john.id)
     @mary_result = mock(TestRequest, :id => "2", :user_id => @john.id + '1')
-    User.should_receive(:find).with(@john.id).and_return(@john)
+    User.should_receive(:find).at_least(:once).with(@john.id).and_return(@john)
   end
 
   it "should let user see her testing result" do
diff --git a/spec/controllers/users_controller_spec.rb b/spec/controllers/users_controller_spec.rb
new file mode 100644
--- /dev/null
+++ b/spec/controllers/users_controller_spec.rb
@@ -0,0 +1,95 @@
+
+require File.dirname(__FILE__) + '/../spec_helper'
+
+describe UsersController, "when a new user registers" do
+
+  before(:each) do
+    # create john
+
+    @john_info = {:login => 'john', 
+      :full_name => 'John John', 
+      :email => 'john@space.com'}
+    @john = User.new(@john_info)
+
+    @john_activation_key = "123456"
+
+    @john.should_receive(:activation_key).
+      any_number_of_times.
+      and_return(@john_activation_key)
+
+    get :new
+    response.should render_template('users/new')
+  end
+
+  it "should show the new form again when user information is invalid" do
+    User.should_receive(:new).with(any_args()).and_return(@john)
+    @john.should_receive(:activated=).with(false)
+    @john.should_receive(:valid?).and_return(false)
+    @john.should_not_receive(:save)
+
+    post :register, :login => @john_info[:login], 
+                    :full_name => @john_info[:full_name], 
+                    :email => @john_info[:email]    
+
+    response.should render_template('users/new')
+  end
+
+  it "should create unactivated user and send e-mail with activation key" do
+    User.should_receive(:new).with(any_args()).and_return(@john)
+    @john.should_receive(:activated=).with(false)
+    @john.should_receive(:valid?).and_return(true)
+    @john.should_receive(:save).and_return(true)
+
+    smtp_mock = mock("smtp")
+    smtp_mock.should_receive(:send_message) do |msg,fr,to|
+      to.should == [@john_info[:email]]
+      msg.index(@john_activation_key).should_not be_nil
+    end
+
+    Net::SMTP.should_receive(:start).
+      with(any_args()).
+      and_yield(smtp_mock)
+
+    post :register, :login => @john_info[:login], 
+                    :full_name => @john_info[:full_name], 
+                    :email => @john_info[:email]
+
+    response.should render_template('users/new_splash')    
+  end
+  
+  it "should create unactivated user and return error page when e-mail sending error" do
+    User.should_receive(:new).with(any_args()).and_return(@john)
+    @john.should_receive(:activated=).with(false)
+    @john.should_receive(:valid?).and_return(true)
+    @john.should_receive(:save).and_return(true)
+
+    smtp_mock = mock("smtp")
+    smtp_mock.should_receive(:send_message).
+      and_throw(:error) 
+
+    Net::SMTP.should_receive(:start).
+      with(any_args()).
+      and_yield(smtp_mock)
+
+    post :register, :login => @john_info[:login], 
+                    :full_name => @john_info[:full_name], 
+                    :email => @john_info[:email]
+
+    response.should render_template('users/email_error')    
+  end
+  
+  it "should activate user with valid activation key" do
+    login = @john_info[:login]
+    User.should_receive(:find_by_login).
+      with(login).
+      and_return(@john)
+    @john.should_receive(:valid?).and_return(true)
+    @john.should_receive(:activated=).with(true)
+    @john.should_receive(:save).and_return(true)
+
+    get :confirm, :login => login, :activation => @john_activation_key
+
+    response.should render_template('users/confirm')
+  end
+
+end
diff --git a/spec/models/site_spec.rb b/spec/models/site_spec.rb
--- a/spec/models/site_spec.rb
+++ b/spec/models/site_spec.rb
@@ -4,39 +4,44 @@
 describe Site do
 
   before(:each) do
-    start_time = Time.local(2008,5,10,9,00)
+    start_time = Time.local(2008,5,10,9,00).gmtime
     @site = Site.new({:name => 'Test site',
                        :started => true,
                        :start_time => start_time })
+    @site.stub!(:start_time).
+      any_number_of_times.
+      and_return(start_time)
+    @site.stub!(:started).any_number_of_times.and_return(true)
   end
   
   it "should report that the contest is not finished when the contest time limit is not set" do
     Configuration.should_receive(:[]).with('contest.time_limit').
       and_return('unlimit')
-    Time.should_not_receive(:now)
     @site.finished?.should == false
   end
 
   it "should report that the contest is finished when the contest is over" do
     Configuration.should_receive(:[]).with('contest.time_limit').
-      and_return('5:00')
-    Time.should_receive(:now).and_return(Time.local(2008,5,10,14,01))
-    @site.finished?.should == true
-  end
+    and_return('5:00')
+    Time.stub!(:now).
+      and_return(Time.local(2008,5,10,14,01).gmtime)
+    @site.finished?.should == true end
 
   it "should report if the contest is finished correctly, when the contest is over, and the contest time contains some minutes" do
     Configuration.should_receive(:[]).twice.with('contest.time_limit').
       and_return('5:15')
-    Time.should_receive(:now).
-      and_return(Time.local(2008,5,10,14,14),Time.local(2008,5,10,14,16))
+    Time.stub!(:now).
+      and_return(Time.local(2008,5,10,14,14))
     @site.finished?.should == false
+    Time.stub!(:now).
+      and_return(Time.local(2008,5,10,14,16))
     @site.finished?.should == true
   end
 
   it "should report that the contest is not finished, when the time is exactly at the finish time" do
     Configuration.should_receive(:[]).with('contest.time_limit').
       and_return('5:00')
-    Time.should_receive(:now).and_return(Time.local(2008,5,10,14,00))
+    Time.stub!(:now).and_return(Time.local(2008,5,10,14,00))
     @site.finished?.should == false
   end
 
diff --git a/spec/models/user_spec.rb b/spec/models/user_spec.rb
--- a/spec/models/user_spec.rb
+++ b/spec/models/user_spec.rb
@@ -48,7 +48,48 @@
   it "should not accept invalid activation key" do
     @john.verify_activation_key("12345").should == false
   end
-  
+end
+
+describe User, "when re-register with the same e-mail" do
+
+  before(:each) do
+    @mary_email = 'mary@in.th'
+    
+    @time_first_register = Time.local(2008,5,10,9,00).gmtime
+
+    @mary_first = mock_model(User, 
+                             :login => 'mary1', 
+                             :password => 'hello', 
+                             :email => @mary_email,
+                             :created_at => @time_first_register)
+    @mary_second = User.new(:login => 'mary2', 
+                            :password => 'hello', 
+                            :email => @mary_email)
+    User.stub!(:find_by_email).
+      with(@mary_email, {:order => "created_at DESC"}).
+      and_return(@mary_first)
+  end
+
+  class User
+    public :enough_time_interval_between_same_email_registrations
+  end
+
+  it "should not be allowed if the time interval is less than 5 mins" do
+    time_now = @time_first_register + 4.minutes
+    Time.stub!(:now).and_return(time_now)
+
+    @mary_second.enough_time_interval_between_same_email_registrations
+    @mary_second.errors.length.should_not be_zero
+  end
+
+  it "should be allowed if the time interval is more than 5 mins" do
+    time_now = @time_first_register + 6.minutes
+    Time.stub!(:now).and_return(time_now)
+
+    @mary_second.enough_time_interval_between_same_email_registrations
+    @mary_second.errors.length.should be_zero
+  end
+
 end
 
 describe User, "as a class" do