iMessage is an integrated messaging app for all users of Apple's ecosystem. From your Mac, you can send messages to your friends who use your iPhone and ̵
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Setting Up Messages on Your Mac
You do not need an iCloud (or even an iPhone) to use iMessage, but you need an Apple ID. If you already have an iCloud account, the email you used to sign in is your Apple ID.
Launch the Messages app from the Dock, your Applications folder, or use Command + Space to search for it. When you start the app for the first time, you will be asked to log in. If you do not have an Apple ID, you can click "Create New Apple ID" below to sign in. Otherwise, log in with your existing Apple ID.
After logging in, open the Message settings by clicking Messages on the menu bar and selecting "Preferences" – or by pressing Command + Comma.
The iMessage tab contains the options for managing your iMessage account. Make sure your phone number or email is listed under "You are for Otherwise, you will not receive messages on your Mac.
 If you have two contacts, such as your Apple ID and phone number, you can post messages for both accounts At the bottom, you can choose which one you prefer when notifying new people Using an email-based iMessage account is like using a phone-based account You can send a message to anyone using iMessage, including their phone number. But only phone accounts can notify Android users via SMS.
Before closing this window, you need to make sure "Enable messages in iCloud" is turned on so that all old messages sync properly with your Mac. You should enable this on all your devices.
CONNECTION: To sync your iMessages with all your Apple devices
If your phone number does not appear in the message settings , you need to make sure iMessage is enabled on your phone. On the phone, go to Settings> Messaging and make sure iMessage is turned on. If it is not, the message "Use your Apple ID for iMessage" appears, which you must click and sign in with the account you are using on your Mac.