WTF is the point of inserting an A-R header if you are not willing to
take responsibility for what you have done by signing it?
And why should anyone else believe your A-R if you have omitted that
elementary step?
Because, if you've followed the RFC defining it, the border MTA has removed any
others present that could possibly be misinterpreted by internal agents.
You're not required to sign them, but it's not a bad idea.
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