When I send an email using the GMail API, I get an Access Token for the user to whom the message is to be sent and then when sending the message, I put some value in the Fro
No, what you are looking for is a bulk email sending service. Checkout sendgrid , Amazon AWS SES, mandrill or if you want to stick with Google, this. You could of course run your own postfix server (although I'm assuming you were using gmail api for deliverability in the first place.