Question
In what situations is Google's test domain alias used?
Answer
The test domain alias (domains ending with .test-google-a.com) is typically used to test whether emails can be received in Google Workspace.
Test email addresses cannot be used for sending email tests.
Reference: Test Email Addresses (Google Workspace Admin Help)
Additionally, when checking the DMARC Dashboard in Email DLP, the results for SPF/DKIM/DMARC on test domain aliases (domains ending with .test-google-a.com) will be "Not Applicable".
This is because, as mentioned earlier, it is not possible to specify a test domain alias as the Env-From address (actual email sender address) for sending emails due to Google's specifications, resulting in a "Not Applicable" status.