How to take off email on iMessage

• Check that you have the latest software for your iOS device and your Mac.
• On your iPhone, go to Settings > Messages. Make sure that iMessage is on. You might need to wait for it to activate.
• Tap Send & Receive.
• If you see "Use your Apple ID for iMessage," tap it and sign in with your Apple ID. If not, skip this step.Under "You can be reached by iMessage at," make sure that there are check marks beside your phone number and Apple ID.*
• For help with FaceTime, go to Settings > FaceTime and use the same steps.

If you still need help, follow these steps on all of your Apple devices:

1. On every Mac that you own, go to Messages > Preferences > Accounts. Click iMessage in the left column, then click Sign Out. Then sign out in the FaceTime app under FaceTime > Preferences.
2. On every iPhone, iPad, and iPod that you own, go to Settings > Messages > Send & Receive and sign out of your Apple ID. Do the same thing in Settings > FaceTime.
3. Use the beginning of this section to turn on iMessage and link your Apple ID to your phone number. Then use the same Apple ID to sign back in to Messages and FaceTime on your other devices.
4. If you still need help, change your Apple ID password. Then turn on iMessage, link your Apple ID to your phone number, and try again.

Add or remove your phone number to iMessage or FaceTime on your Mac, iPad, and iPod touch - Apple Support

Its not up to you, its up to them. They need to have a contact with your E-Mail address and your name for messages to show a name when they receive an iMessage from you. You cannot force your name on someone else's iPhone.

Alternatively, if your friend has a contact with your number instead of your E-Mail, you can go to Settings->Messages->Send & Receive->"Start New Conversations From", and make sure your number is selected there instead of your E-Mail.