[chatmasta]

can't it just live on the sender's device until the receiver is online? think about sending an iMessage on the subway... "undelivered" doesn't mean that your message is sitting on Apple servers somewhere. it means it's still on your phone and you can try sending it again when you have a better uplink.

[shalmanese]

When you can't reach Apple, it's undelivered. But there's also the case where you can reach Apple but Apple can't reach the recipient. Then, the message sits on Apple's servers until the recipient can be reached.