I registered my domain foo.com through google domains, and then I setup email forwarding so that emails sent to firstname.lastname@example.org go to email@example.com, but now I want to send email from firstname.lastname@example.org.
Well, I went through the support channels at Google domains — so you don’t have to.
To set up your Gmail to send using an alias, 2-Step Verification must first be enabled (you can disable it right afterwards). To enable 2-Step Verification, follow the instructions on this link. Once enabled, follow these steps:
1. Log into your Gmail account.
2. In Gmail, click your username or user icon in the upper right corner to bring up the user menu.
3. Click ‘My Account’
4. In the Google account screen, click the Sign in and security tab.
5. In the Sign in box, click the Settings for App Passwords. Please note that you must have 2-Step Verification enabled for the App passwords option to be available. If it is not, click Edit and enable 2-Step Verification. Then continue to set the App password.
6. In the App passwords box, select Mail for the app, select Other for the device.
7. Enter the name of your domain for the “other” device, and click Generate.
8. The Generated app password box will display a 16-character password. Copy this password. You will need it when you add your new send-as (forwarded) account.
9. Return to your Gmail screen.
10. In the top right corner, click the Settings button.
11. Select Settings from the drop down menu.
12. In the Settings screen, click the Accounts and Import tab.
13. Scroll down to Send mail as and click Add another email address you own.
14. In the first Add another email address box, enter the name you want recipients of your email to see (such as “Support Team” or “Sales” or any other name for this contact) and the forwarded email address you are setting up.
15. Click Next Step.
16. In the second Add another email address box, change the values in fields to enter the following: smtp.gmail.com (SMTP Server), 465 (Port), Gmail email address (Username), and the password you copied in Step 8.
17. Click Add Account. If you see an error message, check to make sure you have entered the SMTP server, Port, Username, and Password correctly.
18. After you have successfully added the account, return to Gmail. You will see a message from Gmail Team with the subject Gmail Confirmation: Send Mail As and the address you have just added. Follow the instructions in the message to confirm the email address.
19. When you send mail from your Gmail account, click the triangle next to your From address to choose to send the message from the account you just added.
For more information on sending mail from your forwarded address in Gmail, see the Gmail Help center topic: “Send mail from a different address or alias”
I hope that helps! Hopefully this article will be irrelivant soon enough, once Google fixes this. Until then…