send both emails

app/mailers/devise_notify_mailer.rb

@@ -38,8 +38,12 @@ class DeviseNotifyMailer < Devise::Mailer
     username = record.email
     if email_changed?(record)
       username = record.unconfirmed_email
-      send_email_changed_to_old_email(record)
-      send_confirmation_email(record.unconfirmed_email, record, token, username)
+      if someone_else_changed_email?(record)
+        send_email_changed_to_old_email(record)
+        send_email_changed_to_new_email(record, token)
+      else
+        send_confirmation_email(record.unconfirmed_email, record, token, record.unconfirmed_email)
+      end
     end
     send_confirmation_email(record.email, record, token, username)
   end
@@ -55,10 +59,12 @@ class DeviseNotifyMailer < Devise::Mailer
     Rails.application.credentials[:email_allowlist] || []
   end
 
-  def send_email_changed_to_old_email(record)
+  def someone_else_changed_email?(record)
     # Do not send if user changed own email
-    return unless record.versions.last.actor != record && record.versions.last.changeset.key?("unconfirmed_email") && FeatureToggle.new_email_journey?
+    FeatureToggle.new_email_journey? && record.versions.last.actor != record && record.versions.last.changeset.key?("unconfirmed_email")
+  end
 
+  def send_email_changed_to_old_email(record)
     return true if intercept_send?(record.email)
 
     send_email(
@@ -71,6 +77,22 @@ class DeviseNotifyMailer < Devise::Mailer
     )
   end
 
+  def send_email_changed_to_new_email(record, token)
+    return true if intercept_send?(record.email)
+
+    link = "#{user_confirmation_url}?confirmation_token=#{token}"
+
+    send_email(
+      record.email,
+      User::FOR_NEW_EMAIL_CHANGED_BY_OTHER_USER_TEMPLATE_ID,
+      {
+        new_email: record.unconfirmed_email,
+        old_email: record.email,
+        link:,
+      },
+    )
+  end
+
   def email_changed?(record)
     record.confirmable_template == User::CONFIRMABLE_TEMPLATE_ID && (record.unconfirmed_email.present? && record.unconfirmed_email != record.email)
   end

spec/requests/users_controller_spec.rb

@@ -1698,7 +1698,7 @@ RSpec.describe UsersController, type: :request do
               before do
                 other_user.legacy_users.destroy_all
 
-                allow(FeatureToggle).to receive(:new_email_journey?).and_return(true)
+                allow(FeatureToggle).to receive(:new_email_journey?).and_return(false)
               end
 
               it "does not update the password" do
@@ -1729,8 +1729,6 @@ RSpec.describe UsersController, type: :request do
                 end
 
                 it "sends a new flow emails" do
-                  expect(notify_client).to receive(:send_email).with(email_address: other_user.email, template_id: User::CONFIRMABLE_TEMPLATE_ID, personalisation:).once
-                  expect(notify_client).to receive(:send_email).with(email_address: new_email, template_id: User::CONFIRMABLE_TEMPLATE_ID, personalisation:).once
 
                   expect(notify_client).to receive(:send_email).with(
                     email_address: other_user.email,
@@ -1741,6 +1739,16 @@ RSpec.describe UsersController, type: :request do
                     },
                   ).once
 
+                  expect(notify_client).to receive(:send_email).with(
+                    email_address: other_user.email,
+                    template_id: User::FOR_NEW_EMAIL_CHANGED_BY_OTHER_USER_TEMPLATE_ID,
+                    personalisation: {
+                      new_email:,
+                      old_email: other_user.email,
+                      link: include("/account/confirmation?confirmation_token="),
+                    },
+                  ).once
+
                   patch "/users/#{other_user.id}", headers:, params:
                 end
               end