Validate email for common typos and one-time email providers
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EmailInquire is a library to validate email for format, common typos and one-time email providers.



Before a user is a user, they are a visitor. And they must register to be so. What if they makes a typo while entering their email address during the registration ? If they didn't notice, you just lost them. They won't be able to sign in next time.

Your users :

  • may not be as tech savvy as you;
  • may not remember exactly their email address;
  • may make a typo while typing their email address (very very common on a mobile keyboard).

While we can't do so much for the name part of the email address, for the domain part, we can be smart!

And also, we don't want for users to use one-time email addresses (also called burner or disposable email addresses).

Supported cases

Format error. This doesn't strictly follow RFC 5322, it aims at validating email that will be deliverable on Internet. It also takes into account length of email, name part and domain part as per SMTP specification.

  • => invalid
  • => invalid
  • => invalid
  • foo@localhost => invalid
  • foo@ => invalid
  • secré => invalid
  • => valid
  • ...

One char typo for 43 common email providers (worldwide and from France, United Kingdom and USA):

  • => hint
  • => hint
  • => hint
  • => hint
  • ...

ccTLD specificity, like United Kingdom domains:

  • foo.couk => hint
  • => hint
  • => hint
  • => ok!
  • ...

...and same thing with & domains.

Providers with an unique domain:

  • => hint
  • => hint
  • => hint
  • => hint
  • => hint
  • => hint
  • ...

3764 one-time email providers (a.k.a. burners, or disposable email source):

  • => invalid
  • ...

Custom invalid domains: Add your own invalid domains:

# in config/initializers/email_inquire.rb
EmailInquire.custom_invalid_domains << ""
  • => invalid


Add this line to your application's Gemfile:

gem 'email_inquire'

And then execute:

$ bundle

Or install it yourself as:

$ gem install email_inquire


Use EmailInquire.validate(email), you'll get a EmailInquire::Response that represents weither or not the email address is valid or may contain a mistake.

Methods of EmailInquire::Response:

Method Description Possible values
#email The validated email address ""
#status The status of the validation :valid :invalid or :hint
#valid? Is the email valid ? true or false
#invalid? Is the email invalid ? true or false
#hint? Is there a possible mistake and you have to show a hint to the user ? true or false
#replacement A proposal replacement email address for when status is :hint "" or nil


A valid case:

response = EmailInquire.validate("")
response.status # :valid
response.valid? # true

An invalid case:

response = EmailInquire.validate("")
response.status   # :invalid
response.valid?   # false
response.invalid? # true

A hint case:

response = EmailInquire.validate("")
response.status      # :hint
response.valid?      # false
response.hint?       # true
response.replacement # ""

A custom invalid case:

# in config/initializers/email_inquire.rb
EmailInquire.custom_invalid_domains << ""


response = EmailInquire.validate("")
response.status   # :invalid
response.valid?   # false
response.invalid? # true


I think it's important to just offer a hint to the user and to not automatically replace the maybe faulty email address in the form.

A "Did you mean xxx@yyy.zzz ?" has the following advantages:

  • user remains in charge: we could have hinted against a perfectly valid email;
  • user is educated;
  • mini whaoo effect;

This "Did you mean xxx@yyy.zzz ?" is better being actionable, and appearing to be so: a click or tap on it should replace the email by the suggestion.

  +---------------------------------------+  +---------+
  |                     |  | Sign Up |
  +---------------------------------------+  +---------+
    Did you mean ?

Note that you could even have this validation for your Sign In form...


After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to


Bug reports and pull requests are welcome on GitHub at


The gem is available as open source under the terms of the MIT License.