After the latest Smartermail upgrade, we are noticing an issue in our Sophos XGD Firewall Email Protection, where the error "Verifying recipient address with callout" - "Address unknown" appears.

This did not happen before, at least not that we noticed. Has anyone else experienced something similar?

Example, from Sophos XGS logs

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.xxx.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

Thanks