This plugin detects one-time email addresses (disposable email, trashmail, mailinator) and helps to keep your userbase and comments clean.
This plugin does NOT submit email addresses. I do not run this service to collect your subscribers data.
Before the data is sent to http://www.block-disposable-email.com the domain part is separated. So only the domain part is sent. For further information see the mentioned website.
First of all I try to have minimum downtime. That's why there are currently 3 servers at different locations (UK, US, AT) waiting for your requests. For further information see http://www.block-disposable-email.com/faq.php
And yes, even if the service is down your users are able to leave comments.
If your credits are running low you will be informed by email. If the credits are used up you get an additional email. In case you do not have any credits left the service will always respond with an OK (like the used domain is valid to subscribe).
In other words: even if you do not have any credits left your subscribers are allowed to subscribe (or leave comments or whatever). But users subscribing with trashmail / disposable email addresses are also allowed ...
Please see http://www.block-disposable-email.com/pricing.php if you need more than the 200 free credits a month.
What Captcha cannot block are human subscribers using one-time email-addresses. It is bad to have such addresses in your userbase for several reasons. And yes, it is easy to block *.ru addresses, known domains as trashmail.net, and some others - but they are changing continuously. This service currently detects about 3.000 domains. So maybe it is a good alternative for your manually maintained blocklist.
This should be happen very rarely. In this case I kindly ask you to report this mistake.
Sure. Have a look at http://www.block-disposable-email.com/usage.php. There are several documents for the json, txt and php-serialized api.