APN服务将消息排队 - 但Apple不保证交付所有消息。当用户离线时，只有来自应用程序的 last 消息将保留在队列中。此外，旧邮件可能会被删除。

The APN service will queue messages up -- but Apple doesn't guarantee delivery of all messages. Only the last message from an application will be kept in the queue when the user is offline. Additionally, old messages may be deleted.

本地和推送通知编程指南

Apple推送通知服务
包括默认的质量服务
（QoS）组件，执行
存储转发功能。如果APNs
尝试发送通知但是b $ b设备处于离线状态，则QoS会存储
通知。它在
设备上每个应用程序仅保留一个
通知：最后一个通知从该应用程序的提供程序收到
。
当离线设备稍后
重新连接时，QoS会将
存储的通知转发给设备。
QoS会在删除之前保留
限制期间的通知。

Apple Push Notification Service includes a default Quality of Service (QoS) component that performs a store-and-forward function. If APNs attempts to deliver a notification but the device is offline, the QoS stores the notification. It retains only one notification per application on a device: the last notification received from a provider for that application. When the offline device later reconnects, the QoS forwards the stored notification to the device. The QoS retains a notification for a limited period before deleting it.