How do I change my email name on the mail app?

You can remove that mail account from system preferences > internet accounts Change Internet Accounts settings on Mac - Apple Support

Delete Account

Remove the account and turn off all its features.

This option is available after you click a specific account in the list of accounts set up on your Mac.

Hi King5557,

From what you described in your post, we recommend that you try the steps in the link below to learn how to change the address you're sending emails from.

Choose a default email address to send mail from on iCloud.com

Complete the steps in the section below to perform the recommended troubleshooting steps via the link above.

If you create an email alias or create an email address with a custom domain, you can select one to be the default email address you send mail from.

You can also select which email addresses you want to be able to send mail from in addition to the default address. The selected addresses appear in the From pop-up menu when you create a new message. See Write and send email in Mail on iCloud.com.

1) In Mail on iCloud.com, click  at the top of the Mailboxes list, then choose Preferences.

2) Click Composing, click the “Set a default address” pop-up menu, then choose an email address.

3) In the list of addresses below, select the ones you want to be able to send from in iCloud Mail.

4) Click Done.

We recommend the above steps because they will show you how to choose a default email address from which to send mail.

If you’re still experiencing the same issue, then check out the link here: Change settings in Mail on Mac

Please let us know the outcome after giving the above steps a try.

Thanks for using the Apple Support Communities.

Cheers!

Hi King5557,

Thanks for following up. We'd like to clarify an important point. We see you posted in the iCloud.com section of the forum, and also mentioned the Mail app. Can you clarify whether you're using the iCloud website or if you're using the Mail app? If you are using the Mail app, which device and software version are you using? This will help work out what steps you need to take.

Also, you mentioned you changed your Apple ID. Are you saying you started using an entirely new address, or did you change it using the steps in this link? Change your Apple ID - Apple Support

The best steps are going to depend on exactly what's happening and the device you're using, but if you're on an iPhone and no longer want to use the account in question at all, you could tap Settings > Mail > Accounts and then tap the account and turn it off.

If that doesn't answer your question, let us know the answers to the above.

Take care.