Why isn't my iphone texting other iphones through imessage?

It's updated and so is the person I'm texting. I'm able to text some iphones but not other ones. Even iphones that are new text through the SMS thing. Why?

You should check the setting of you iMessage whether they are properly configured or not. It requires an email address thorugh which the other person can contact you. Make sure that it is properly inserted and is verified. Next, go to the contact of the person you are wishing to iMessage with. Make sure that you have their email inserted in the contact which they are using as their iMessage contact. This should solve the problem. If the problem still persists, try giving your phone a proper restore via iTunes. This solves most of the problems.
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