Improve the regexp a bit more.

lib/devise.rb

@@ -108,7 +108,7 @@ module Devise
   # an one (and only one) @ exists in the given string. This is mainly
   # to give user feedback and not to assert the e-mail validity.
   mattr_accessor :email_regexp
-  @@email_regexp = /\A[^@]+@[^@]+\z/
+  @@email_regexp = /\A[^@]+@([^@\.]+\.)+[^@\.]+\z/
 
   # Range validation for password length
   mattr_accessor :password_length

test/models/validatable_test.rb

@@ -29,7 +29,7 @@ class ValidatableTest < ActiveSupport::TestCase
     assert user.invalid?
     assert_not_equal 'is invalid', user.errors[:email].join
 
-    %w{invalid_email_format 123 $$$ () ☃}.each do |email|
+    %w{invalid_email_format 123 $$$ () ☃ bla@bla.}.each do |email|
       user.email = email
       assert user.invalid?, 'should be invalid with email ' << email
       assert_equal 'is invalid', user.errors[:email].join