Oneall has notified that K1 has exceeded the Freemium plan of 2500 unique users per year.
Which means it's going to cut off new users, or cut off K1 all together, not really sure.
Which means it's back to relying on the crappy Yahoo mail service for verification. Kureha is aware that it's dropping emails, there is just too many emails that need to be sent, and free email providers basically deems it as spam.
Before someone suggest upgrading the service plan, or using a paid email service, let it be known that K1 simply does not have the resources. There is just nothing that can be done.
Here's an idea of the funds K1 is running on.

That's technically not even enough to maintain K1.
Other than the first adfly ad on outbound links, no other ads are implemented by K1. Judging from the statistics, most of the people block them anyways. All other ads are inserted by the users providing the links and are not affiliated with K1 in any way.
On the plus side, the domain is currently paid for till Q1 2026 thanks to previous contributor donations. So barring some catastrophic hardware failure or Kureha's death, K1 should limp along until at least 2026.