Unfortunately, you cannot delete a message from both your and the recipient's iPhone once it is sent using the default iMessage or SMS app. However, some third-party apps like WhatsApp or Telegram allow you to delete messages from both sides within a specific time frame.
Unsend a message
You can undo a recently sent message for up to two minutes after sending it. Touch and hold the message bubble, then tap Undo Send. A note confirming that you unsent the message appears in both conversation transcripts: yours and your recipient's.
You can only take back a message within two minutes of sending it. The recipient can read your message before you unsend it. If you unsend a message, it will disappear from the recipient's screen, but they'll be notified that you unsent it.
If they delete the individual message (or the entire chat/conversation) in iMessage, it will change the final Read to a delivered. This is the reason why a Read will turn into a Delivered after the fact.
If the person you are texting has iOS 16, a message will appear saying you unsent a text message. The person you're texting won't know what that message was, as long as they didn't see a preview of that text when the original iMessage was sent.
If you delete a conversation or message, it cannot be recovered. This action is permanent.
If you delete before the send is complete, usually it will not send but because data is sent in batches, it may have been delivered before the phone receives confirmation of delivery. The best way is to instantly put the phone in airplane mode, then delete the message.
Originally Answered: If you have deleted messages on iMessage would the other person still have them and be able to see them? Yes, when you delete a message thread, you are only deleting your copy of the thread. It has no impact on other people in the conversation.
If you can't add or remove someone in a group message
You can only remove someone if the group has four or more people, and everyone is using an Apple device, like an iPhone or iPad. You can only add someone to a group message if they're using an Apple device.
In addition to the requirement of having iOS 16 to 'unsend' a message using an iOS device, Apple advises in Use Messages on your iPhone or iPad - Apple Support that "If you unsend a message to someone on an older version of iOS, iPad OS, or macOS, your contact might still see the message."
Deleting messages changes only your own Messages conversations, not those of your recipients.
Deleting a message: Press and hold on the "undesired" text message. A Quick Actions menu will appear on your screen.
From Chats, open a Messenger conversation. Tap and hold the message you'd like to unsend and select More. Tap Remove.
The recipient can read your message before you unsend it. If you unsend a message, it will disappear from the recipient's screen, but they'll be notified that you unsent it.
This week, Apple released its latest operating system, iOS 16, which lets users edit an iMessage up to five times within 15 minutes after sending it and unsend any message up to 2 minutes after it's sent. Users just need to tap and hold the sent message, then select “edit” or “undo send.” But there are some caveats.
How to Tell if Text Messages were Deleted. To tell if text messages were deleted from your iPhone, what you will need is PhoneRescue for iOS. Because it allows you to scan your iPhone, then you can preview all messages and iMessage on your iPhone, including deleted ones.
It will not. Delivered means the message is now on the recipients device. If the recipient's is off/not connected to the internet, the iMessage will not reach their device and will not register as delivered.
You can only unsend an iMessage within 2 minutes of sending it. To unsend an iMessage, simply long-press on the message and select the Undo Send option.