When setting up an identity to send from a Google Workspace (formerly Google Apps / Google Suite) domain alias, you may find that the messages you send either still appear to be from your primary Google Workspace account, or as sent 'via' it. To fix this, please follow this guide to make sure everything is set up correctly on Google's end:

• First, please follow this guide to ensure that everything is set up correctly on Google's end.
• Next, you will need to create an App Password in Google, and use it as your password in Mailbird.
  Please refer to this article by Google for guidance on the process.
• In Mailbird, the identity should be created with the alias address in the email field, set to send through Google's SMTP server, and the credentials set to your main Google Workspace email and the App Password you created above.