https://www.cyrusimap.org/imap/concepts/features/event-notif...
It's too bad that, assuming that documentation is still up to date, Apple doesn't allow smaller IMAP mail providers to integrate with the push notification service.
We would love to be able to send push notification to native apple Mail app for our users but we never wrapped our head around the whole certificate thing. (And Apple was... unhelpful).
Would love to have support on this! Are you available? Let me know (nicolo.benigni@qboxmail.com)
ABE and ABM both use the same technology so it's pretty much exactly how Apple intends it to be used. There used to be someone hosting a shared CA for this, but it because cumbersome to deal with third parties not loading the CRL and not using OSCP.