BTW: I don't think validating by cron or manually is feasible for userbases larger than a few thousand. The cron runs 6 times per day and validates 25 addresses per run, so 150 per day. Thats 4500 per month. We have hundreds of thousands of accounts. I can do that trough CLI, though that is still quite slow as it uses single checks instead of bulk checking trough API. The API response speed differs quite a lot between providers.
Monthly subscriptions of some providers are much cheaper than prepaid credits. This can safe hundreds of bucks. But these subscriptions often limit the number of validations per day to a certain number of thousands per day. Which means that we would need to run CLI every day for many weeks.
I'm really happy that you've added this functionality. If its possible to implement bulk/batch API checks instead of single checks then that would make it much easier to use.