When you start a new iMessage conversation, it may not come from the phone number or Apple ID you expect, which may cause confusion for the recipient. Here's how to make sure that new conversations use the correct phone number or e-mail address.
This setting has been in iOS and macOS for years, but may not be configured properly by default. If you prefer to use your email address to start a new iMessage conversation, you need to make sure all your devices are configured correctly. If this is not the case, you run the risk of fragmenting the recipient's messages, potentially having multiple conversations with the same person, but using two different numbers or email addresses.
It's this risk of confusion that Apple has tried to prevent by multiple updates, and although the situation is definitely better today than it was a few years ago, nothing is perfect.
Make sure new iMessage conversations are started with a consistent number or email address, which is part of the battle, so here's how to make sure your devices are all on the same wavelength.
Changing the number or email address where new conversations start on iPhone and iPad
To begin, open the Settings application and press "Messages."
Then scroll down the screen and press "Send and Receive".
On the next screen, under "Start new conversations from", you will see the starting points available for new iMessage conversations. You will probably see your phone number and at least one email address, starting with your Apple ID. Tap the one from which you want to start new conversations.
Change the number or e-mail address from which new conversations start on a Mac
Open the Messages application and click "Messages" in the menu bar, followed by "Preferences."
Click the "iMessage" tab to see the options associated with the mail service.
Finally, click the drop-down list under "Start New Conversations From" and select the number or e-mail address you want to use.
By making sure your new iMessage conversations use the correct phone number or e-mail address, you avoid confusion for the recipient. If you have already been in several conversations with the same person, it would be a good setting for both of you.