3CX DLL-Sideloading attack: What you need to know

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Recipient address rejected: Access denied error on Email Gateway


I am currently in trial mode and doing some email sending with a test domain. It is a hosted on MS 365

I believe I have everything setup correctly but I am receiving this error when sending from an outside address

Any ideas on what may be wrong 

Reporting-MTA: dns; googlemail.com
Arrival-Date: Thu, 11 Aug 2022 16:25:56 -0700 (PDT)
X-Original-Message-ID: <CANfQ=SLg+sdRvreawv14+mF1W4yvQMd5GNyBsO+F13hdsqw8uQ@mail.gmail.com>

Final-Recipient: rfc822; testuser@xxxx.com
Action: failed
Status: 5.7.1
Remote-MTA: dns; mx-01.eml100syd.ctr.sophos.com. (, the server for
the domain arlpay.com.)
Diagnostic-Code: smtp; 554 5.7.1 <testuser@xxxx.com>: Recipient address rejected: Access denied
Last-Attempt-Date: Thu, 11 Aug 2022 16:25:58 -0700 (PDT)



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