I completely understand the importance of receiving all of your messages, ariibabe! In the event that your data is turned off and your iMessage is on, it is possible that all messages will not be received as iMessages travel over data. It is only guaranteed to receive all of these messages while you and the user sending the messages are both connected to WiFi/cellular data with iMessage turned on. The other parties sending the message can also go in their settings under messages and enable the option, "Send as SMS if iMessage is not available". This is best way to receive these messages as text messages if you are not connected to WiFi or cellular data.
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