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Email forwarding : 550 5.7.1 Command rejected

Hi, we have a problem with forwarding emails. Exchange 2013 on Prem. Using Email Security on Sophos Central. 

This seems to have come up on here before, but I cant find a solution.  Any help appreciated.



I use exchange to forward emails on for a user to an external account at

I can email the external account from our domain and they can email in.

If I email from any other exernal account, say I get the following error:

Subject: Delivery Failure Notification

 Sophos XG Firewall was unable to send the following mail:


MessageID: <LNXP265MB250800947BB98F138EDDAD85B6E69@LNXP265MB2508.GBRP265.PROD.OUTLOOK.COM>

Sent on: 2022-04-07 12:39:27

 Mail delivery to following recipients failed: - 550 5.7.1 Command rejected


Resent-From: <>

Received: from ExchangeServer (10.10.) by  exchangeserver (10.10.) with Microsoft SMTP Server (TLS)  id 15.0.847.32; Thu, 7 Apr 2022 12:42:47 +0100

Received: from

( by Exchange.domain1 (10.10. with Microsoft  SMTP Server id 15.0.847.32 via Frontend Transport; Thu, 7 Apr 2022 12:42:28


Received: from

( [])      by (Postfix) with ESMTP id

4KZ00l6CnfzPjdl        for <>; Thu,  7 Apr 2022 11:44:39

+0000 (UTC)



dkim=pass header.d=domain3 header.from=domain3;  dmarc=pass (recordpolicy=quarantine) header.from=domain3

Received-SPF: pass;

client-ip=; envelope-from=< >;;

X-Sophos-Product-Type: Gateway

X-Sophos-Email-ID: c65874521353416d8dbc3e35fd16a1a1

Received: from

( []) (using

TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client  certificate requested) by (Postfix)  with ESMTPS id 4KZ00c6Rhsz9rwG for <>; Thu,  7

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