In D4557#129937, @ashoat wrote:

Thanks for making these changes! One question for you – do you think we need to specify notification.priority in D4113 as well?

Apple docs are strict about background notifications: https://developer.apple.com/documentation/usernotifications/setting_up_a_remote_notification_server/sending_notification_requests_to_apns?language=objc#2947607. Priority other than 5 is an error. When it comes to other notification types, priority 10 is a good choice if we expect immediate reaction from user. Otherwise notification delivery will be based on power consumption. Personally I would not change priority here. Apple is not strict about it and we used to send notifications with priority 10 for some time without any issues.

And does notification.mutableContent = true require a specific notification.pushType, similar to notification.contentAvailable?

Setting notification.mutableContent = true means notification is of type alert and is expected to be processed by NotificationService before being shown to user (https://developer.apple.com/documentation/usernotifications/unnotificationserviceextension?language=objc). If you look at the code, we already specify correct push type: https://github.com/CommE2E/comm/blob/master/keyserver/src/push/send.js#L492