Our list covers established providers rather than every domain in circulation. Commercial lists carry tens of thousands of entries and are still incomplete, because the supply is effectively unbounded — a new provider needs one domain and an afternoon.
So treat a clean result as an absence of evidence rather than evidence of absence. If your signup flow genuinely depends on a durable address, confirm it by sending mail and requiring a click. That is the only check that proves anything, and it works regardless of which provider the address belongs to.
If you are deciding what to accept at signup, the argument for verifying rather than predicting is set out in why websites block disposable email. Checking a full address rather than a domain? The email validator runs this check alongside five others.