Hello @OSørensen, thank you for your patience here, we are getting a 551 response from your server on the SMTP side. Our team has suggested that this is some type of authentication or permission issue on the SMTP side.
Both articles contain more information, at the moment this is all the visibility we have on this issue from our end. I would recommend you please share that with your email administrator and continue to troubleshoot this on your end. We cannot provide further insight since we do not manage the email servers.
I have looked at the post, and tried various alternatives, with limited luck I am afraid. I have further comfirmed the SMTP server and ports, which works for other services, including Outlook.
Would greatly appreciate any input regarding possible next steps here @PamCotton