5 Ways to Implement Email Validation in Rails

Ensuring email addresses are valid in a Rails application is key to maintaining data integrity and a smooth user experience. We'll explore five ways to implement this validation, providing working code snippets for each. We will also examine the pitfalls of these traditional methods and show how Abstract API addresses them.

How to Implement Email Validation in Rails

Here are four common methods to validate email formats directly within a Rails application. Each approach uses different tools, from built-in constants to specialized gems for more advanced checks.

Inline Regular Expression

This method uses pure ActiveModel format validation. It defines a regular expression, or regex, as a constant named "EMAIL_REGEX" inside the User model to check the email's structure. The code validates that the email attribute is present and matches this pattern.

This approach keeps the application's dependency graph small because it does not require an external gem, a DNS call, or extra memory allocations. The regex pattern itself can be adjusted to fit specific domain requirements, such as to allow or disallow sub-domains.

class User < ApplicationRecord
  EMAIL_REGEX = /\A[\w+\-.]+@[a-z\d\-.]+\.[a-z]+\z/i
  validates :email, presence: true, format: { with: EMAIL_REGEX }
end

Built-in URI::MailTo::EMAIL_REGEXP

Ruby's standard library includes a predefined constant, "URI::MailTo::EMAIL_REGEXP", for email validation. Since Rails automatically picks up this constant, you can use it directly in your model validations without any setup.

This expression mirrors the one used by browsers for fields with "type=email", which ensures server-side and client-side validations share the same logic. The code simply applies this built-in regex to the email attribute.

class User < ApplicationRecord
  validates :email, format: { with: URI::MailTo::EMAIL_REGEXP }
end

The activemodel-email_address_validator Gem

This gem provides a plug-and-play validator for ActiveModel. After you add the gem to your Gemfile, you can use the "email_address: true" validator in your model. The gem supports internationalization and rejects local-only addresses.

It can also perform a DNS lookup for a domain's Mail Exchange (MX) record, which indicates if the domain can receive email. You can extend its functionality with custom patterns to enforce specific policies. The code shows basic validation, a DNS MX lookup, and a custom rule.

# Gemfile
gem 'activemodel-email_address_validator'

# Model
class User < ApplicationRecord
  validates :email, email_address: true                 # basic
  validates :email, email_address: { mx: true }          # DNS MX lookup
  validates :email, email_address: { with: /…/ }         # custom rule
end

The email_address Gem

The "email_address" gem is a full parser that tokenizes and normalizes email addresses. It can provide a canonical form for uniqueness checks, a redacted form for privacy, and even offers ActiveRecord type casting.

The gem supports multiple validation modes, autocorrects capitalization, and strips tags from addresses like "user+tag@example.com". It also integrates with I18n for custom error messages. The code shows how to add the validator to the model.

# Gemfile
gem 'email_address'

# Model
class User < ApplicationRecord
  validates_with EmailAddress::ActiveRecordValidator, field: :email
end

Challenges of Email Validation in Rails

While these methods offer some control, they introduce significant challenges. Simplified regex patterns, limited scope, and maintenance overhead often lead to both false positives and rejected valid emails.

• Simplified patterns, like inline regex or the built-in URI::MailTo::EMAIL_REGEXP, willfully violate the RFC-5322 spec. They fail to account for edge cases like apostrophes or quoted local parts, which results in the rejection of valid addresses.
• Most Rails patterns, especially custom regex, lack support for internationalized mailboxes. They fail to match Unicode characters or punycoded domains, so the system incorrectly rejects valid global email addresses and confuses international users.
• Syntax validation alone does not confirm an email's reachability. Methods like inline regex check format but cannot detect if a mailbox exists or if the domain accepts mail. This means syntactically correct addresses can still bounce.
• The email landscape constantly evolves with new TLDs and disposable domains. Hard-coded patterns, common in inline regex validations, quickly become outdated. Without frequent manual updates, they block legitimate users and accept throwaway addresses.