refactor: move lib/postal/smtp_server to app/lib/smtp_server

spec/lib/smtp_server/client_spec.rb

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+
+module SMTPServer
+
+  describe Client do
+    let(:ip_address) { "1.2.3.4" }
+    subject(:client) { described_class.new(ip_address) }
+  end
+
+end