If you want to use alternative email address instead of your original gmail address, you need to provide details for an SMTP server which will be used to send the mail.
The first action you should do is → Settings → Accounts → Add another email address like below
Then you will see popup window like below
When you click "Next Step", you will see following:
If you have smtp server available, you can use it. Otherwise, please follow below
- For SMTP Server, put
smtp.gmail.com
- For Username, your full Gmail address including
@gmail.com
- For password, provide an App Password generated in Google Accounts at https://security.google.com/settings/security/apppasswords
- Leave Secured connection using TLS selected as is.
- Add Account