Implement email validation

[JohnRDOrazio]

Email validation will be done mainly by sending a validation link. However it can be useful to filter out valid email formats from the start, just in case someone accidentally types in an invalid email format.

Browsing on stackoverflow, I found a mention of the valid_email2 gem which could help some:

Don't use a regular expression for email address validation. It's a trap. There are way more valid email address formats than you'll think of. However! The mail gem (it's required by ActionMailer, so you have it) will parse email addresses — with a proper parser — for you:

require 'mail'
a = Mail::Address.new('foo@example.com')

This will throw a Mail::Field::ParseError if it's a non-compliant email address. (We're not getting into things like doing an MX address lookup or anything.)

If you want the good ol' Rails validator experience, you can make app/models/concerns/email_validatable.rb:

require 'mail'

module EmailValidatable
  extend ActiveSupport::Concern

  class EmailValidator < ActiveModel::EachValidator
    def validate_each(record, attribute, value)
      begin
        a = Mail::Address.new(value)
      rescue Mail::Field::ParseError
        record.errors[attribute] << (options[:message] || "is not an email")
      end
    end
  end
end

and then in your model, you can:

include EmailValidatable
validates :email, email: true

As Iwo Dziechciarow's comment below mentions, this passes anything that's a valid "To:" address through. So something like Foo Bar <foo.bar@example.com> is valid. This might be a problem for you, it might not; it really is a valid address, after all.

If you do want just the address portion of it:

a = Mail::Address.new('Foo Bar <foobar@example.com>')
a.address
=> "foobar@example.com"

As Björn Weinbrenne notes below, there are way more valid RFC2822 addresses than you may expect (I'm quite sure all of the addresses listed there are compliant, and may receive mail depending system configurations) — this is why I don't recommend trying a regex, but using a compliant parser.

If you really care whether you can send email to an address then your best bet — by far — is to actually send a message with a verification link.