fix(smtp-server): fixes proxy protocol

spec/lib/smtp_server/client/proxy_spec.rb

@@ -0,0 +1,28 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+
+module SMTPServer
+
+  describe Client do
+    let(:ip_address) { nil }
+    subject(:client) { described_class.new(ip_address) }
+
+    describe "PROXY" do
+      context "when the proxy header is sent correctly" do
+        it "sets the IP address" do
+          expect(client.handle("PROXY TCP4 1.1.1.1 2.2.2.2 1111 2222")).to eq "220 #{Postal::Config.postal.smtp_hostname} ESMTP Postal/#{client.trace_id}"
+          expect(client.ip_address).to eq "1.1.1.1"
+        end
+      end
+
+      context "when the proxy header is not valid" do
+        it "returns an error" do
+          expect(client.handle("PROXY TCP4")).to eq "502 Proxy Error"
+          expect(client.finished?).to be true
+        end
+      end
+    end
+  end
+
+end