Kureha is aware of some mails are not arriving at their intended destinations, the problem is, there is no fix, yahoo mail just sucks.
Unless Kureha finds a better email provider, it'll be a hit n miss. Some people are receiving their activation emails while some aren't.
As it is, there are hundreds of membership applications per week, Kureha simply cannot sift through them one at a time, and opening new memberships to non-activations will open the flood gates to all the spam account problems Kureha One has had in the past.
Non activated accounts are deleted every 24hrs or when Kureha gets around to purging them.