You can edit the "From" or "Sending" name, the name displayed to recipients of your email messages, and your reply-to email address, the address where replies to your email messages will be sent, in your "Mail Options".To edit these settings:
Mail Options Menu: Mail Accounts
Mail Accounts: Selecting Email Address
In the "Sending name" box, enter the name exactly as you would like it to appear in the "From:" line of your outgoing messages. Then click the Save button.
Mail Accounts: Sending Address and Save Button
Note: The From name may not contain special characters, such as the @ symbol.
If you leave the "Reply-to address" field blank, the return address of your outgoing messages will automatically display your Yahoo! Business Email address. If you would like recipients of your messages to reply to a different email address, enter that address in the "Reply-to address" field. Your reply-to email address may not exceed 40 characters.
Note: You must enter a "Sending" name. If you leave this box blank, the previous entry or your default name, the name you gave when you registered with Yahoo!, will appear and your other changes will not be saved.