Let's say I had the email address like putin-crab@?????????.?? How to validate that address in rails 3.1? My Model(i use Mongoid): #encoding: utf-8 class User include Mongoid::Document field :email, :type => String validates :email, :presence => true, :format => { :with => RFC822::EMAIL } end For validations reqexp i use gem https://github.com/dim/rfc-822 in rails console (normal email): ruby-1.9.2-p290 :001 > usr = User.new( :email => "[email protected]" ) => #<User _id: 4ec627cf4934db7e4d000001, _type: nil, email: "[email protected]"> ruby-1.9.2-p290 :002 > usr.valid? => true in rails console (fu@#ing email): ruby-1.9.2-p290 :003 > usr = User.new( :email => "putin-crab@?????????.??" ) => #<User _id: 4ec627f44934db7e4d000002, _type: nil, email: "putin-crab@?????????.??"> ruby-1.9.2-p290 :004 > usr.valid? Encoding::CompatibilityError: incompatible encoding regexp match (ASCII-8BIT regexp with UTF-8 string) from /home/username/.rvm/gems/ruby-1.9.2-p290@rail31/gems/activemodel-3.1.1/lib/active_model/validations/format.rb:9:in `=~' from /home/username/.rvm/gems/ruby-1.9.2-p290@rail31/gems/activemodel-3.1.1/lib/active_model/validations/format.rb:9:in `!~' from /home/username/.rvm/gems/ruby-1.9.2-p290@rail31/gems/activemodel-3.1.1/lib/active_model/validations/format.rb:9:in `validate_each' from /home/username/.rvm/gems/ruby-1.9.2-p290@rail31/gems/activemodel-3.1.1/lib/active_model/validator.rb:153:in `block in validate' from /home/username/.rvm/gems/ruby-1.9.2-p290@rail31/gems/activemodel-3.1.1/lib/active_model/validator.rb:150:in `each' from /home/username/.rvm/gems/ruby-1.9.2-p290@rail31/gems/activemodel-3.1.1/lib/active_model/validator.rb:150:in `validate' from /home/username/.rvm/gems/ruby-1.9.2-p290@rail31/gems/activesupport-3.1.1/lib/active_support/callbacks.rb:302:in `_callback_before_13' from /home/username/.rvm/gems/ruby-1.9.2-p290@rail31/gems/activesupport-3.1.1/lib/active_support/callbacks.rb:404:in `_run_validate_callbacks' from /home/username/.rvm/gems/ruby-1.9.2-p290@rail31/gems/activesupport-3.1.1/lib/active_support/callbacks.rb:81:in `run_callbacks' from /home/username/.rvm/gems/ruby-1.9.2-p290@rail31/gems/mongoid-2.3.3/lib/mongoid/callbacks.rb:42:in `block in run_callbacks' from /home/username/.rvm/gems/ruby-1.9.2-p290@rail31/gems/mongoid-2.3.3/lib/mongoid/callbacks.rb:67:in `call' from /home/username/.rvm/gems/ruby-1.9.2-p290@rail31/gems/mongoid-2.3.3/lib/mongoid/callbacks.rb:67:in `run_cascading_callbacks' from /home/username/.rvm/gems/ruby-1.9.2-p290@rail31/gems/mongoid-2.3.3/lib/mongoid/callbacks.rb:41:in `run_callbacks' from /home/username/.rvm/gems/ruby-1.9.2-p290@rail31/gems/activemodel-3.1.1/lib/active_model/validations.rb:212:in `run_validations!' from /home/username/.rvm/gems/ruby-1.9.2-p290@rail31/gems/activemodel-3.1.1/lib/active_model/validations/callbacks.rb:53:in `block in run_validations!' from /home/username/.rvm/gems/ruby-1.9.2-p290@rail31/gems/activesupport-3.1.1/lib/active_support/callbacks.rb:390:in `_run_validation_callbacks' from /home/username/.rvm/gems/ruby-1.9.2-p290@rail31/gems/activesupport-3.1.1/lib/active_support/callbacks.rb:81:in `run_callbacks' from /home/username/.rvm/gems/ruby-1.9.2-p290@rail31/gems/mongoid-2.3.3/lib/mongoid/callbacks.rb:42:in `block in run_callbacks' from /home/username/.rvm/gems/ruby-1.9.2-p290@rail31/gems/mongoid-2.3.3/lib/mongoid/callbacks.rb:67:in `call' from /home/username/.rvm/gems/ruby-1.9.2-p290@rail31/gems/mongoid-2.3.3/lib/mongoid/callbacks.rb:67:in `run_cascading_callbacks' from /home/username/.rvm/gems/ruby-1.9.2-p290@rail31/gems/mongoid-2.3.3/lib/mongoid/callbacks.rb:41:in `run_callbacks' from /home/username/.rvm/gems/ruby-1.9.2-p290@rail31/gems/activemodel-3.1.1/lib/active_model/validations/callbacks.rb:53:in `run_validations!' from /home/username/.rvm/gems/ruby-1.9.2-p290@rail31/gems/activemodel-3.1.1/lib/active_model/validations.rb:179:in `valid?' from /home/username/.rvm/gems/ruby-1.9.2-p290@rail31/gems/mongoid-2.3.3/lib/mongoid/validations.rb:70:in `valid?' from (irb):4 from /home/username/.rvm/gems/ruby-1.9.2-p290@rail31/gems/railties-3.1.1/lib/rails/commands/console.rb:45:in `start' from /home/username/.rvm/gems/ruby-1.9.2-p290@rail31/gems/railties-3.1.1/lib/rails/commands/console.rb:8:in `start' from /home/username/.rvm/gems/ruby-1.9.2-p290@rail31/gems/railties-3.1.1/lib/rails/commands.rb:40:in `<top (required)>' from script/rails:6:in `require'