iMessage often fails to send SMS on non-iOS device Since iOS 10.1, my iPhone often fails to send SMS. After sending, it waits, then display the red (!), saying "not delivered"


it seems to only happen on non-iPhone recipients
most of time (everytime??), my recipient still get my message (in spite of the not delivered warning)
someone told me "why do you always send your messages twice?".


How this correct this issue?
This could be down to people previously using an iPhone and having their number registered with iMessage, and then moving to a non-iOS device. In this case, your phone is still trying to send the message over the iMessage platform even though the recipient can't receive it. They can check and de-register here.