Whitelable Outgoing Mail from Google App Engine

Question

I'm looking into whitelabling outgoing email being sent from a Google App Engine Application - in other words, when I send an email from myapp.com and the client's company is mycompany, the from email address should show david@mycompany.com

The only way I've seen so far that it can be done is by adding those email addresses as application admins / developers (viewers?) into the application permissions section.

Firstly, is there a limit to the number of admins I can add and secondly is there some way that I can restrict their access to the application's Cloud Console ? Does each admin address I add need to be using Google Apps for their domain in order for whitelabling to work?

Is there a better way of doing it?

I've looked at using Compute Engine, but Compute Engine only allows sending via gmail or using external APIs. I see Google is heavily promoting SendGrid as their partner, but SendGrid charges $20 per whitelable address per month and their pricing is around 5 times more expensive than Google's $1 per 10000 emails.

Can whitelabling be achieved using Amazon SES?

Answer 1

Apparently, if you use Google Auth, your application can send from any email that has authorized your application. This means if you have any user authenticate with Google OAuth, you may send on their behalf.

However, sending from SendGrid or Amazon SES, may be easier.

With SendGrid may send from any sender without authenticating their address. SendGrid's "whitelabeling" (the $20 a month thing) is on a per domain basis and allows for DKIM & SPF signing of your messages, however this is not a requirement (as you can send without this). As a Google App Engine customer, you get 25,000 free emails a month, you may also use the SendGrid Lite Plan to send at $1 per 10,000.

Amazon SES does require sender authentication, although this is pretty simple to do. You can verify a domain or authenticate individual senders by sending them an email and having them click a link. Amazon will do DKIM and SPF signing for each domain you verify. With SES you may send to 2,000 emails a day on the AWS Free Usage Tier, with additional messages (or messages sent after free usage tier expires) costing $1 per 10,000

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In the interest of full disclosure, I should mention, I'm a SendGrid employee.