You have a sign-up form on your website, to prevent spamming, trolls, and perhaps only allow a trial version or freebie per user.
The user doesn't want to give you his real e-mail.
There are many many websites, where users can instantly generate a random e-mail, for example: [email protected]ga.
They give you this disposable instantly generated e-mail instead of their real one!
As soon as they sign-up, or get whatever they want from you, they never bother about that e-mail address again.
Even if you require e-mail validation, they can simply click your link when it is received, and then never read that e-mail again.
You now have the fake e-mail [email protected] in your database, and the user can easily repeat the same thing hundreds of times.
And with literally hundreds of different domains.
It's of course fine to allow temporary disposable e-mail addresses if you want to, but it really depends on your target demographic and what services you offer.
If you have a voting system, comments, or allow free trials based on e-mail addresses, it's not as simple. Are you okay with the fact that it's so easy to generate fake e-mail addresses, and download unlimited trials, vote multiple times, or difficulty to block spammers and trolls?
But, if they can always generate unlimited e-mail addresses via Hotmail or Yahoo, why should you care? There is much bigger work involved in generating "real" e-mail addresses than fake disposable temporary e-mail addresses. Many time, if it's too much of a hazzle, they will eventually stop trying.
There are hundreds of domains being used for temporary disposable e-mails, and it's a big job to blacklist them all, and new ones are being added regularly.
Here are a few domains which our API recently blocked automatically: