Email Rejected, using Protect - Email in XGS

Hello,

in the last few days I have noticed that certain emails are not being delivered, and I observed in the Sophos XGS 126 smtp_mail.log that the emails are being rejected. The senders and recipients exist and are known.

This issue started occurring, at least as I have been informed, after the latest firewall update XGS126 (SFOS 20.0.1 MR-1-Build342) 

Mail Logs in GUI I get Status

2024-06-26 11:35:23.217Z [4225] [209.85.221.53] F=<sender_A@gmail.com> R=<my.email@acme.com> Verifying recipient address with callout
2024-06-26 11:35:23.220Z [4225] H=mail-wr1-f53.google.com [209.85.221.53]:42212 I=[xxx.xxx.xxx.xxx]:25 Ci=4225 X=TLS1.3:TLS_AES_256_GCM_SHA384:256 CV=no SNI=mail.corpnaga.net F=<sender_A@gmail.com> rejected RCPT <my.email@acme.com>: Address unknown
2024-06-26 11:35:23.258Z [4225] H=mail-wr1-f53.google.com [209.85.221.53]:42212 I=[xxx.xxx.xxx.xxx]:25 Ci=4225 incomplete transaction (QUIT) from <sender_A@gmail.com>
2024-06-26 11:35:23.258Z [4225] SMTP connection Ci=4225 from mail-wr1-f53.google.com [209.85.221.53]:42212 I=[xxx.xxx.xxx.xxx]:25 D=0.818s closed by QUIT



2024-06-26 13:35:09.093Z [25823] SMTP connection from [195.149.xx.xxx]:7896 I=[xxx.xxx.xxx.xxx]:25 Ci=25823 (TCP/IP connection count = 0)
2024-06-26 13:35:09.736Z [25823] [195.149.xx.xxx] F=<sender_B@someserver.com> R=<my.email@acme.com> Verifying recipient address with callout
2024-06-26 13:35:09.739Z [25823] H=kpedge.someserver.com [195.149.xx.xxx]:7896 I=[xxx.xxx.xxx.xxx]:25 Ci=25823 X=TLS1.2:ECDHE-RSA-AES256-GCM-SHA384:256 CV=no F=<sender_B@someserver.com> rejected RCPT <my.email@acme.com>: Address unknown
2024-06-26 13:35:09.749Z [25823] H=kpedge.someserver.com [195.149.xx.xxx]:7896 I=[xxx.xxx.xxx.xxx]:25 Ci=25823 incomplete transaction (QUIT) from <sender_B@someserver.com>
2024-06-26 13:35:09.753Z [25823] SMTP connection Ci=25823 from kpedge.someserver.com [195.149.xx.xxx]:7896 I=[xxx.xxx.xxx.xxx]:25 D=0.660s closed by QUIT

I have currently disabled Recipient verification in Spam protection.
I am wondering what might be wrong and how I should address this issue?

Thank you for your help.