When sending out the test email, headers are not correct, causing email to bounce. Got the following from my smtp provider:
"From header sender domain not verified (enhancecp.co.uk) On your Sending"
This should be the control panel domain, not enhance.
You're right the test email doesn't obey the branding settings. We will improve this. In the meantime just avoid ticking the box for the test message to be sent and instead generate a user invite or a forgot password link to verify that your system generated email config is working.
Adam Hopefully it is fixed soon. Since it is one of the first things it asks you to do. The onboarding should be the smoothest part, imo.