while this is not a perfect way to prevent abuse of service, we do want
to avoid getting spammed with fake accounts. Creating a valid email
account is significantly more cumbersome than using a disposable email
address.
Currently the list of blacklisted domains is extracted from
https://github.com/disposable/disposable
and it is refreshed after every 24 hours.
This exposes a few more env vars for configuration &
bypasses the Subscription backend
so each user is Pro by default. This is required because there won't be
any mechanism for the user to upgrade. We'll also have to disable a few
things on the client side to avoid confusion.
