So after switching to my new iPhone 6s, I have been sending messages through iMessage. I haven't had any major issues. What has occurred though is that the messages send with the blue bubble (informing me that they are sending as iMessages) and the recipient receives the message and is able to respond without any issue. But the actual messages never displays the words "delivered" under them. While this isn't a major issue as they are sending without any problem, I am wondering why the words "delivered" do not show up.
P.S. the words "delivered" appear for the recipient when they respond to me.