FIX: Use correct URL for unsubscribe (#10077)

app/mailers/subscription_mailer.rb

@@ -9,6 +9,6 @@ class SubscriptionMailer < ActionMailer::Base
                 template: "unsubscribe_mailer",
                 site_title: SiteSetting.title,
                 site_domain_name: Discourse.current_hostname,
-                confirm_unsubscribe_link: "#{Discourse.base_url}/unsubscribe/#{unsubscribe_key}"
+                confirm_unsubscribe_link: email_unsubscribe_url(unsubscribe_key, host: Discourse.base_url)
   end
 end

spec/mailers/subscription_mailer_spec.rb

@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+
+describe SubscriptionMailer do
+  fab!(:user) { Fabricate(:user) }
+
+  subject { SubscriptionMailer.confirm_unsubscribe(user) }
+
+  it "contains the right URL" do
+    expect(subject.body).to include("#{Discourse.base_url}/email/unsubscribe/#{UnsubscribeKey.last.key}")
+  end
+end