A quick note on validating email addresses in Rails.

Rails gives you a couple of clean options here — a built-in regex approach that covers most cases, and a gem if you need deeper validation (MX record checks, disposable email detection, etc.).

  1. 1

    Built-in format validation (usually enough)

    Rails 7.1+ ships a URI::MailTo::EMAIL_REGEXP constant you can reference directly:

app/models/user.rb Ruby 
class User < ApplicationRecord
  validates :email,
    presence: true,
    uniqueness: { case_sensitive: false },
    format: { with: URI::MailTo::EMAIL_REGEXP, message: "must be a valid email address" }
end

On older Rails, use a simple regex:

app/models/user.rb Ruby 
VALID_EMAIL_REGEX = /\A[^@\s]+@[^@\s]+\.[^@\s]+\z/

validates :email,
  presence: true,
  format: { with: VALID_EMAIL_REGEX }
  1. 2

    Normalise the email before saving

    It’s good practice to downcase and strip whitespace so User@Example.com and user@example.com are treated as the same address:

app/models/user.rb Ruby 
before_validation :normalise_email

private

def normalise_email
  self.email = email.to_s.downcase.strip
end
  1. 3

    Deep validation with the truemail gem

    If you need to verify the domain actually has MX records (catches typos like @gamil.com), add the gem:

Gemfile Ruby 
gem "truemail"
config/initializers/truemail.rb Ruby 
Truemail.configure do |config|
  config.verifier_email = "hello@yourdomain.com"
  config.validation_type_for = { "gmail.com" => :regex }
end

Then validate on demand:

email.rb Ruby 
result = Truemail.validate("user@example.com")
result.result.valid?   # => true / false

For most apps, Option 1 + 2 is plenty. Reach for truemail when you need to cut down on bounces on a transactional email flow.

References