Cloud FireStore and Cloud Functions can be easily used to save user details when a new user creates an account. An email can also be sent easily using an external service like Mailgun.
Yandex.Mail for Domains is a free service provided by Yandex. After verifying your domain name ownership, you will get 1000 email accounts with 10 GB space for free.
Yandex Metrica is a free Analytics service similar to Google Analytics.
It has a cool user session replay feature that allows to see how users are using a particular website. It basically records users sessions and then replays it.