Diff for testing between 1 and 2

+ 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. Ususally existing DKIM signatures should still intact after forwarding.

But you may force the broken DKIM signatures. Place the text "modify" somewhere in the Subject and it will be replacedprepended with "modified""[MODIFIED]: " on forwarding. Your DKIM signature
will will be no longer valid. (weWe assume you sign the RFC5322.Subject header as suggestedadvised by RFC...)[https://tools.ietf.org/html/rfc6376#section-5.4 RFC 6376 - DKIM Signatures]