Feature request: check domain existence on registration

Hi,

I have a small feature request which might be easy to implement:

It would be nice if the plugin checks if the email address is valid upon entry.

I regularly have fails with users registering something like someone@gmeil.com, and even a few spammers registering from mail2.xyz.com (yes, I could prevent that with email confirmation, true).

I guess there is even a PHP function that does this: domain_exists(). Could be easy, as you check the registration already against blocked strings?

Many thanks,
Claus

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