As you properly pointed out, the test message verifies that you configured your Email campaign SMTP settings properly. There's no such test message option in the Advanced settings. However, the same configurations you've set to the Email campaigns settings, should work when you set them through the Advanced settings. I've tested the Registration widget and was able to send a confirmation email without any problems. Take a look at this article
from our documentation and make sure that you're not missing a setting.
All the best,
the Telerik team
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