Right now, it has been opened to "Distinguished Members"[1]:
> We are about 15% done and are ramping up our efforts. In fact, just last week, we have released access to the first (very, very early) preview of Kagi Mail with just bare basics in place to our distinguished members.
> We are about 15% done and are ramping up our efforts. In fact, just last week, we have released access to the first (very, very early) preview of Kagi Mail with just bare basics in place to our distinguished members.
[1]: https://blog.kagi.com/first-three-years