[mantasm]

Interestingly enough, you don't need Apple's support to do that: https://github.com/st3fan/dovecot-xaps-daemon.

Apple didn't have to build an API for them, they simply provided documentation for how to use the existing API.

[microtonal]

Ah, that's nice! Though their blog post at the time seemed to indicate that Apple helped them a bit:

https://blog.fastmail.com/2015/07/17/push-email-now-availabl...