Mail delivery to following recipients failed: 550 5.7.1 Command rejected

Hi, 

trying to forward emails external using Exchange 2013 on Prem.  Sophos Central Email setup.

All emails come in and go out as normal, just Forwarding fails

External emails sent to me from internal and external users are not being forwarded on to an external account:

Mail delivery to following recipients failed: user2@domain2.com - 550 5.7.1 Command rejected

Resent-From: <User1@domain1.com>
Received: from Exchange (10.) by exchange (10.) with Microsoft SMTP Server (TLS) id 15.0.847.32; Thu, 7 Apr 2022 12:42:47 +0100
Received: from inbound-18-216-7-10-us-east-2.prod.hydra.sophos.com
(18.216.7.10) by Exchange.domain1 (IP) with Microsoft SMTP Server id 15.0.847.32 via Frontend Transport; Thu, 7 Apr 2022 12:42:28
+0100
Received: from ip-172-21-100-31.us-east-2.compute.internal
(ip-172-21-100-31.us-east-2.compute.internal [127.0.0.1]) by
inbound-18-216-7-10-us-east-2.prod.hydra.sophos.com (Postfix) with ESMTP id
4KZ00l6CnfzPjdl for <User1@domain1.com>; Thu, 7 Apr 2022 11:44:39
+0000 (UTC)
Authentication-Results: mx-01-us-east-2.prod.hydra.sophos.com;
spf=pass smtp.mailfrom=user3@domain3.com;
dkim=pass header.d=domain3 header.from=domain3; dmarc=pass (recordpolicy=quarantine) header.from=domain3
Received-SPF: pass receiver=mx-01-us-east-2.prod.hydra.sophos.com;
client-ip=40.107.10.84; envelope-from=< user3@domain3.com >;
helo=GBR01-LO2-obe.outbound.protection.outlook.com;
X-Sophos-Product-Type: Gateway
X-Sophos-Email-ID: c65874521353416d8dbc3e35fd16a1a1
Received: from GBR01-LO2-obe.outbound.protection.outlook.com
(mail-lo2gbr01on2084.outbound.protection.outlook.com [40.107.10.84]) (using
TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx-01-us-east-2.prod.hydra.sophos.com (Postfix) with ESMTPS id 4KZ00c6Rhsz9rwG for <user1@domain1.com>; Thu, 7 Apr

I have seen similar discussions on here, but no answers.

any help appreciated.

Thanks