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Outgoing emails from mailflow marked with arc=fail


Regarding to the following discussion I have a question.

We have the same problem. Is there a solution to this now? We use Sophos Mailflow and the error "arc=fail" can be found in all mail headers of all outgoing mails.
If we deactivate the outbound MailFlow, the error disappears. SPF, DKIM and DMARC should be configured correctly.
So whats the problem with the ARC?

I would be grateful for a hint.
Best regards

Here are the latest ARC results:

(The Mail was send from our Microsoft365 to an Google Mail Account)

       dkim=pass header.s=selector1 header.b=yt2KMVaM;
       dkim=pass header.s=v1 header.b=p2rjqMLN;
       arc=fail (signature failed);
       spf=pass ( domain of designates xxxxx as permitted sender);
       dmarc=pass (p=QUARANTINE sp=QUARANTINE dis=NONE)
ARC-Seal: i=2; a=rsa-sha256; s=arcselector9901;; cv=fail;
ARC-Authentication-Results: i=2; 1; spf=pass (sender ip is; dmarc=pass (p=quarantine sp=quarantine pct=100) action=none; dkim=pass (signature was verified); arc=fail (47)

ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901;; cv=none;
ARC-Authentication-Results: i=1; 1; spf=pass; dmarc=pass action=none; dkim=pass; arc=none

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