Any issues with storing emails as down-cased?

Question

From time to time, I notice user emails are duplicated. Even with model validation (app level) to check for uniqueness. I suspect this is related to concurrency concerns.

I've decided to add an index on the db level to address this.

The lower index is probably sensible to have anyway.

Even if we are guaranteeing that emails are lowered on the application level. Database provides a stronger guarantee of consistency.

It may never matter, but having the DB enforce it also can't hurt.

I can put in lots of extra safeguards to maximize the odds that there's never an uppercase character put in from the app side but the app still can't control for data going into the db from other sources, and all that code is prone to developer error, maintenance cost, etc.

class CreateUniqueIndexForUserEmails < ActiveRecord::Migration
  def up
    remove_index :users, :email

    execute <<-SQL
      CREATE UNIQUE INDEX index_users_on_lower_email ON users (LOWER(email));
    SQL
  end

  def down
    execute <<-SQL
      DROP INDEX index_users_on_lower_email;
    SQL

    add_index :users, :email
  end
end

I've also coupled this logic with this block of code in the user model:

def email=(value)
  write_attribute :email, value.downcase
end

Which ensures [email protected] gets re-written as [email protected] (on the app level).

I've read an RFC online, mainly from the pointers at Are email addresses case sensitive? that indicate some email servers care about case sensitivity.

Even still, when I send emails out today. I hardly don't take mind into casing. In fact, I type the email out as down-cased. Email still gets delivered.

Is the RFC something to consider highly? i.e. If user inputs [email protected], app registers email as [email protected]. Will this have any impact on email "deliverability"?

If not, what other concerns should I take into account?

Answer 1

Devise applies downcase on the email attribute, so I think it is not an issue.

See: https://github.com/plataformatec/devise/blob/f7b6d786066cef2f5e8d2ce9c6b6cc83918580eb/test/models/database_authenticatable_test.rb#L17

See other assertions in the Devise test file for transformations to consider.