Requested feature overview description.
Stop the google captcha from resetting if the provided email is not valid, and/or stop blacklisting so many email providers.
Provide a more descriptive message than "this email can not be used" if the provided email is in fact blacklisted, and/or have a public list of blacklisted email providers.
Why would it be useful?
Because according to NotMeNotYou in this thread the solution to the blacklist issues is to "please put up with making a throwaway account via an email you don't care about": but this is pretty hard to do when most major email providers require a phone number for sign up, a lot of those who don't are blacklisted, and there's no way to know which emails will work outside of trial and error.
And trial and error is a pain because of the captcha: if someone has already solved the incredibly slow and annoying google captcha (that continuously lies about the result to get users to do more image recognition for free, because google is google), why would they have to solve it again if their email is not up to some silly standard?
Finally, why blacklist so many email providers in the first place?
Spammers still have to go through the captcha and they probably have no issue buying "legit" email adresses in bulk.
What part(s) of the site page(s) are affected?
The sign up page.