diff --git a/app/controllers/passwordless/sessions_controller.rb b/app/controllers/passwordless/sessions_controller.rb
index ce4face..c5cdc14 100644
--- a/app/controllers/passwordless/sessions_controller.rb
+++ b/app/controllers/passwordless/sessions_controller.rb
@@ -213,9 +213,11 @@ def handle_resource_not_found
     end
 
     def call_after_session_save
-      return if @skip_after_session_save_callback
-
-      if Passwordless.config.after_session_save.arity == 2
+      if @skip_after_session_save_callback
+        if Passwordless.config.send_paranoid_email
+          Mailer.unknown_address(@session).deliver_now
+        end
+      elsif Passwordless.config.after_session_save.arity == 2
         Passwordless.config.after_session_save.call(@session, request)
       else
         Passwordless.config.after_session_save.call(@session)
diff --git a/app/mailers/passwordless/mailer.rb b/app/mailers/passwordless/mailer.rb
index 8cace33..d4af857 100644
--- a/app/mailers/passwordless/mailer.rb
+++ b/app/mailers/passwordless/mailer.rb
@@ -29,5 +29,18 @@ def sign_in(session, token = nil, url_options = {})
         subject: I18n.t("passwordless.mailer.sign_in.subject")
       )
     end
+
+    # sends an email when user attempts to login with unknown address
+    #
+    # @param session [Session] An instance of Passwordless::Session
+    def unknown_address(session)
+      email_field = session.authenticatable.class.passwordless_email_field
+      @email = session.authenticatable.send(email_field)
+
+      mail(
+        to: @email,
+        subject: I18n.t("passwordless.mailer.unknown_address.subject")
+      )
+    end
   end
 end
diff --git a/app/views/passwordless/mailer/unknown_address.text.erb b/app/views/passwordless/mailer/unknown_address.text.erb
new file mode 100644
index 0000000..7201149
--- /dev/null
+++ b/app/views/passwordless/mailer/unknown_address.text.erb
@@ -0,0 +1 @@
+<%= t("passwordless.mailer.unknown_address.body", email: @email ) %>
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 091ee62..1a98f8a 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -28,3 +28,13 @@ en:
 
           Alternatively you can use this link to sign in directly:
           %{magic_link}
+      unknown_address:
+        subject: "Not Registered"
+        body: |-
+          We noticed a login attempt using your email, %{email}.
+
+          If you're seeing this email, that means that you don't currently have an
+          account associated with this email.
+          Maybe you have a different email that's associated with your account?
+
+          If this wasn't you, disregard this email.
diff --git a/lib/passwordless/config.rb b/lib/passwordless/config.rb
index e992e0c..93e367a 100644
--- a/lib/passwordless/config.rb
+++ b/lib/passwordless/config.rb
@@ -50,6 +50,7 @@ class Configuration
     )
 
     option :paranoid, default: false
+    option :send_paranoid_email, default: false
 
     def initialize
       set_defaults!
diff --git a/test/controllers/passwordless/sessions_controller_test.rb b/test/controllers/passwordless/sessions_controller_test.rb
index b0ac305..09d7fd5 100644
--- a/test/controllers/passwordless/sessions_controller_test.rb
+++ b/test/controllers/passwordless/sessions_controller_test.rb
@@ -107,6 +107,22 @@ class << User
       assert_equal "/users/sign_in/#{Session.last!.identifier}", path
     end
 
+    test("POST /:passwordless_for/sign_in -> SUCCESS / not found,
+         paranoid enabled, send paranoid email") do
+      with_config(paranoid: true, send_paranoid_email: true) do
+        post("/users/sign_in", params: {passwordless: {email: "a@a"}})
+      end
+
+      assert_equal 1, ActionMailer::Base.deliveries.size
+      assert_nil Session.last.authenticatable
+
+      assert_equal 302, status
+
+      follow_redirect!
+      assert_equal "/users/sign_in/#{Session.last!.identifier}", path
+    end
+
+
     test("POST /:passwordless_for/sign_in -> ERROR / not found and paranoid disabled") do
       post("/users/sign_in", params: {passwordless: {email: "A@a"}})