When I text 1 person (who also has iphone) the message never says Delivered but the person does get the message. Why doesn't it say delivered like it does to anyone else I text with iMessage?
There are a few possibilities.
This person has iMessage disabled in their settings.
They have an older iPhone that doesn't support iMessage.
They have mobile data turned off, in which case, they would only be able to use iMessage when connected to wifi.