[mccorrinall]

Calendars and emails usually don’t need push to show notifications. Email clients usually use imap streaming (if supported) or just poll your inbox every x minutes.

We are specifically talking about push via GCM / Apple here. Afaik signal opens a websocket in the background if GCM push is not supported. Or at least that’s how it worked a few years ago.

Google Cloud Messaging features (push) only work when you have gapps installed or use an alternative implementation like microg.

I assume that whatsapp also has some kind of fallback strategy built in.