+ TESTING openarc.org provides infrastructure you may use to get familar with ARC. ++ 1. Autoresponder Send a message to echo@openarc.org. You'll receive a response instantly. This response contain the message as received by the service. This allowes you to inspect how !OpenARC validate your sent message. ++ 2. Forwarder Send a message to forward@openarc.org. You'll receive your message /forwarded/ back to you. It's not a new one. Existing DKIM signatures are expected to be still intact after forwarding. But you may forcethe brokenmessage modification to invalidate your existing DKIMsignatures. Place thesignature: Choose the text "modify"somewhere in theas Subject and it will be prepended with "[MODIFIED]: " on forwarding. Your DKIM signature will be no longer valid. We assume you sign the RFC5322.Subject header as advised by [https://tools.ietf.org/html/rfc6376#section-5.4 RFC 6376 - DKIM Signatures]