Meaning of red 'x' in sent text message

[janelle moss]

Sometimes a text i have sent will have a black envelope to the right of it, with a red 'x' in the lower right hand corner of the envelope. I used to think it was there when the person hadn't opened the message yet, but that doesn't seem to be the case. It seems to show up at random and lingers for day/weeks. Can anyone tell me what this means? Thank you.

 

[jerseyboy357]

So you are verifying that the SMS in question was received by the person you sent it to?

 

[cedellh]

A red X means that the message failed to send (or the phone thinks it failed to send)