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Regexes are not enough sometimes. We should go all the way and fully parse the email and knock on the server's door to see if they really have a mailbox.

require 'pre'
validator = Pre::Validator.new
validator.valid? "[email protected]"

Pre by default has built in validators for RFC2822 and DNS MX record verification. Validators can be passed through the :validators option.

require 'pre'
# validate with no domain validation
validator = Pre::Validator.new :validators => :format
validator.valid? "[email protected]" # => true

Pre can take blocks for custom validators

require 'pre'
no_gmail = lambda do |address|
	address !~ /gmail.com$/
end
validator = Pre::Validator.new :validators => [:format, no_gmail]
validator.valid? "[email protected]" # => false

Pre can take any object that implements the valid? method

require 'pre'
class ComplexValidator
	def valid? address
		return true unless address =~ /gmail.com$/
		# do not allow [email protected] 
		address !~ /\+.+@/
	end
end
validator = Pre::Validator.new :validators => [:domain, ComplexValidator.new]
validator.valid? "[email protected]" # => false

Pre can also take alternate configuration for a single address

require 'pre'
validator = Pre::Validator.new :validators => :format
validator.valid? "[email protected]", :validators => lambda { |address|
  address =~ /example.co.nz$/
} # => false

Certain strategies may be more "intense" than others. MX Record lookup and other expensive operations can benefit from providing Pre with a cache store. A cache store must respond to :write(key, val) and :read(key) methods. The cache abstraction layer provided by Rails' ActiveSupport::Cache::Store fits this interface.

require 'pre'
memcache = ActiveSupport::Cache::MemCacheStore.new("localhost", "server-downstairs.localnetwork:8229")
validator = Pre::Validator.new :cache_store => memcache
validator.valid? "[email protected]" # => true

1. Fork
2. Make tests
3. Make changes to lib
4. Ensure tests pass on 1.8/1.9
5. Submit request
6. Smile

• ActiveModel, Mongoid::Document, etc.. integration
• DSL for configuring Pre validation configuration sets

The RFC treetop grammars are pulled from the fantastic mail gem.