fix(message-dequeuer): ensure SMTP endpoints are sent to SMTP sender appropriately

closes #2853

app/lib/message_dequeuer/incoming_message_processor.rb

@@ -163,7 +163,7 @@ module MessageDequeuer
 
       case queued_message.message.endpoint
       when SMTPEndpoint
-        sender = @state.sender_for(SMTPSender, queued_message.message.recipient_domain, nil, servers: [queued_message.message.endpoint])
+        sender = @state.sender_for(SMTPSender, queued_message.message.recipient_domain, nil, servers: [queued_message.message.endpoint.to_smtp_client_server])
       when HTTPEndpoint
         sender = @state.sender_for(HTTPSender, queued_message.message.endpoint)
       when AddressEndpoint

app/models/smtp_endpoint.rb

@@ -47,4 +47,8 @@ class SMTPEndpoint < ApplicationRecord
     routes.each { |r| r.update(endpoint: nil, mode: "Reject") }
   end
 
+  def to_smtp_client_server
+    SMTPClient::Server.new(hostname, port: port || 25, ssl_mode: ssl_mode)
+  end
+
 end