You can send iMessages to people using Apple devices, but not to people using non-Apple devices. In that! case! MMS or SMS will be! automatically selected and sent, so first check whether the device the person you are sending to is an Apple device.
Have you changed your device model?
You need to check if the other person has changed their phone model. As mentioned above, iMessage is a service that can only be used on Apple products such as iPhones and iPads. When changing your phone model from 12 ways agencies are adopting ai an iPhone, you must also unsubscribe from iMessage, but it seems that many people forget to do this. To unsubscribe from iMessage, select “Settings → Messages buy telemarketing data” and switch off the “iMessage” slide key.
If you forget to unlock the phone and switch models, especially when switching from an iPhone to an Android smartphone, the message “Not Delivered” will be displayed. If you find yourself in this situation, first check with the other person to see if they have switched models.
Is the recipient’s iMessage setting enabled?
Enabling iMessage settings is something that should be checked not only by the sender but also by the recipient. Ask the recipient to 1) turn on the iMessage feature and 2) make sure that their phone number and email address are entered correctly.
If the recipient doesn’t have access to the Internet, or there is something wrong with their Internet settings, the clean email message may be sent as an SMS instead, or the “delivered” indicator may take a long time to appear. This is a basic step, but check your Internet connection.