Index: Gemfile
===================================================================
--- Gemfile	(revision 17428)
+++ Gemfile	(working copy)
@@ -14,6 +14,7 @@
 gem "mimemagic"
 gem "mail", "~> 2.6.4"
 gem "csv", "~> 1.0.2" if RUBY_VERSION >= "2.3"
+gem "simpleidn"
 
 gem "nokogiri", "~> 1.8.0"
 gem "i18n", "~> 0.7.0"
Index: app/models/email_address.rb
===================================================================
--- app/models/email_address.rb	(revision 17428)
+++ app/models/email_address.rb	(working copy)
@@ -25,7 +25,7 @@
   after_destroy :destroy_tokens, :deliver_security_notification_destroy
 
   validates_presence_of :address
-  validates_format_of :address, :with => /\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\z/i, :allow_blank => true
+  validates_format_of :address, :with => /\A([^@\s]+)@((?:[-a-z0-9]+\.)+(xn--)?[a-z0-9]{2,})\z/i, :allow_blank => true
   validates_length_of :address, :maximum => User::MAIL_LENGTH_LIMIT, :allow_nil => true
   validates_uniqueness_of :address, :case_sensitive => false,
     :if => Proc.new {|email| email.address_changed? && email.address.present?}
@@ -33,7 +33,9 @@
   safe_attributes 'address'
 
   def address=(arg)
-    write_attribute(:address, arg.to_s.strip)
+    local_part, at, domain = arg.to_s.strip.rpartition('@')
+    ascii_address = at.empty? ? domain : local_part + at + SimpleIDN.to_ascii(domain)
+    write_attribute(:address, ascii_address)
   end
 
   def destroy
Index: test/unit/user_test.rb
===================================================================
--- test/unit/user_test.rb	(revision 17428)
+++ test/unit/user_test.rb	(working copy)
@@ -84,6 +84,12 @@
     assert_equal "foo@bar.com", u.mail
   end
 
+  def test_mail_should_accept_idn
+    u = User.new
+    u.mail = "maeda@испытание.test.テスト"
+    assert_equal "maeda@xn--80akhbyknj4f.test.xn--zckzah", u.mail
+  end
+
   def test_should_create_email_address
     u = User.new(:firstname => "new", :lastname => "user")
     u.login = "create_email_address"