Messages in iCloud stores all your Messages (iMessages and SMS texts), including attachments and images, in your iCloud account and syncs them between devices. Awesome, how do I turn it on?

Messages in iCloud is available to iPhones & iPads running iOS 11.4 and will also be coming to macOS in the 10.13.5 update which will be released shortly.

What does it do?

• All your devices always have the most recent state.
• If you delete a thread, it deletes everywhere.
• If you set up a brand new device, it will have your entire Messages history.
• It also saves space on your devices by storing older messages and attachments in iCloud.
• The new feature maintains Apple's end to end encryption for all your messages and attachments to ensure your privacy.

But didn't my messages already Sync?

Previously the devices all needed to be powered on and connected to the internet at once. If a device was offline, it wouldn’t ever get the messaging changes from your other devices. Also, if you deleted a conversation it would only disappear from the device you’re currently using.

Sounds Awesome, how do I turn it on?

• Makes sure your device is updated to at least iOS 11.4.
• Open the Settings app.
• Tap on your iCloud and Apple ID settings (it’s your name and image at the top).
• Tap on iCloud.
• Toggle Messages on.

Your Mac Tech recommends you are connected to wifi and power for the initial sync (particularly if you have a lot of messages).