There is a problem connecting a Yandex account. According to Yandex technical support, OAuth authorization via the Mozilla Thunderbird mail client is currently unavailable — redirection in this client is configured incorrectly. This issue is on the side of the program developers. You can contact their support service and ask them to correct the settings. For now, we can offer another authorization method for Mozilla Thunderbird — using the application password. To do this, you need to change the authentication type to "Normal Password". For more information on how to do this, see our Help.