Traditional SMS (Short Message Service) and MMS (Multimedia Messaging Service) do not inherently support read receipts as part of their standard protocols. These services are managed by cellular carriers, and any features related to delivery or read receipts are typically carrier-specific enhancements.
On iOS devices, read receipts for SMS/MMS are not a native feature of the standard messaging protocols. If a carrier supports any form of read receipts for SMS/MMS, this functionality is controlled by the carrier, not the device. However, for iMessages (Apple's proprietary messaging service), read receipts are indeed managed by the iOS device, and users can enable or disable them within the device's settings.

iMessage : Read receipts only apply to iMessage conversations when it is enabled or disabled in your settings.
SMS: For regular SMS this be overridden by your Carrier.
Make sure the messages you're sending and receiving are within the iMessage platform.
SMS Read receipts will depend on three things.
- Carrier's feature capability for Read Receipts
- Carrier's traffic to handle (You will notice that all the SMSs do not have Read receipts in the pic below)
You will notice that all the SMSs do not have Read receipts in the pic below Only the last one SMS received has.
