I have had this issue for a long time.....went in to my iPhone setting and made the recommended changes.....will yes out later today and see if it works for my iPhone 6 Plus
Thanks to BelgoTes on the great find on this. I can confirm that for anyone having this issue the fix is to check the settings he details above under settings -> messages -> send and receive. For me the fix was to ensure that neither sending OR receiving end had the "start new conversations from" setting as an email address. For me the fix was to uncheck all except the phone number on both sender and receiver phones, quitting imessage app, test sending and replying from the car, and then re-checking the email addresses you'd like to be able to receive from again on both phones.