fix: add X-Envelope-From header

Adds X-Envelope-From header to incoming SMTP messages containing the
original envelope sender address.

Cherry-picked from postalserver/postal PR postalserver#3512

Co-authored-by: Mortza81 <Mortza81@users.noreply.github.com>
Co-authored-by: openhands <openhands@all-hands.dev>

Author: openhands-agent

app/lib/smtp_server/client.rb

@@ -419,6 +419,10 @@ def data(_data)
       received_header = ReceivedHeader.generate(@credential&.server, @helo_name, @ip_address, :smtp)
                                       .force_encoding("BINARY")
 
+      envelope_header = "<#{@mail_from}>"
+      @data << "X-Envelope-From: #{envelope_header}\r\n"
+      @headers["x-envelope-from"] = [envelope_header]
+
       @data << "Received: #{received_header}\r\n"
       @headers["received"] = [received_header]
 

spec/lib/smtp_server/client/data_spec.rb

@@ -75,6 +75,7 @@ module SMTPServer
             client.handle("This is some content for the message.")
             client.handle("It will keep going.")
             expect(client.instance_variable_get("@data")).to eq <<~DATA
+              X-Envelope-From: <test@test.com>\r
               Received: from test.example.com (1.2.3.4 [1.2.3.4]) by #{Postal::Config.postal.smtp_hostname} with SMTP; #{Time.now.utc.rfc2822}\r
               Subject: Test\r
               \r