Use Messages in iCloud
With Messages in iCloud, all the messages you send, receive, or delete are updated on all your devices automatically. Keeping your messages in iCloud also helps you save space on your Mac.
To use Messages in iCloud, you need macOS 10.13.5 or later and iOS 11.4 or later, and you need to be signed in to iMessage using the same Apple ID on every device where you want to use it.
Turn on Messages in iCloud
Make sure you’re signed in to iCloud using the same Apple ID you use to sign in to Messages.
Turn on two-factor authentication for iCloud, if you haven’t already.
In Messages, choose Messages > Preferences, click Accounts, then select iMessage in the Accounts list.
Select “Enable Messages in iCloud.”
The messages from your other devices that use the same Apple ID appear on your Mac.
Important: Depending on how many messages you have, it may take some time for all of them to appear. You can send and receive messages during that time.
Turn off Messages in iCloud
You can turn off Messages in iCloud just for this Mac or for all devices where you use it.
Choose Messages > Preferences, click Accounts, then select iMessage in the Accounts list.
Deselect “Enable Messages in iCloud.”
Choose one of the following:
Disable All: Turns off Messages in iCloud for all your devices. Messages will no longer be stored in iCloud and will instead be stored on each device.
Disable This Device: Turns off Messages in iCloud for your Mac only. Messages on your Mac will no longer be stored in iCloud; messages on any other device where Messages in iCloud is turned on will continue to be stored in iCloud.
To make sure you’re seeing the latest messages in iCloud on your Mac, choose Messages > Preferences, click Accounts, click iMessage in the Accounts list, then click Sync Now.