Q: Someone I know is visiting from outside the United States, therefore they can only receive my iMessages when they are connected to Wi-Fi. However, if I send anything and it doesn’t indicate “Delivered,” would deleting it cancel the message’s sending or will they receive it when they reconnect to Wi-Fi?
A: In general, the communication will not be cancelled. When you press the ‘Send’ button on an iMessage, your iOS device is pretty well committed to delivering it, and it will keep trying until it either fails (i.e. there is no network coverage) or it is sent. In fact, deleting a message while it’s being processed by “Sending…” will only remove your local copy on that device; the message will still be transmitted and appear on other devices that you’ve enabled for your iMessage account, such as a Mac or iPad.
Furthermore, if you have the “Send as SMS” option activated in your Messages Settings on your iPhone, any messages that cannot be delivered via iMessage will be sent as regular text messages. Even removing them from the Messages discussion view will not stop the process. There’s no way to stop a message from being delivered after it’s been sent, but if it fails to send, you’ll notice an error icon and the message will be marked as “Not Delivered.”
The message will not be resent at this point unless you tap the error icon and choose to manually resend it. Note that this usually only occurs if your iPhone is out of network range and unable to send the message to Apple’s servers. If you’ve ever sent a message that you want to cancel right away, you can try putting your iPhone in Airplane Mode, but you’ll usually have to wait about five minutes before it gives up trying, and you’ll have to do this before the message is sent out in the first place — often only a few seconds if you’re only sending a simple text message.