I don't know if you are using a gmail account or not, but I am now also unable to send Admin email from WeatherCat and Google has removed the third-party app authentication option described in my above post date September 1, 2023. Furthermore, Google announced in January 2024, "Google will end support for Less Secure Apps on September 30, 2024." Unless the app, in this case, WeatherCat, supports Google's OAuth service, no more gmail access. In my case, it appears my Google account has been shoved over early. I cannot find a way to send Admin emails from WeatherCat.
I would love to hear from more WeatherCatters. Can you still send a successful email test from WeatherCat|Settings|Email|Test Now?