The Mail tab in General Settings allows you to configure how WHMCS sends and manages email. You can choose and configure your mail provider, configure email headers and footers, and more.
You can choose from several supported mail providers for your WHMCS installation, including Google™, Mailgun, Microsoft®, PHP Mail, SendGrid, SMTP, or SparkPost.
You can configure Google as your mail provider using SMTP. This requires creating an app in the Google Cloud console and configuring SMTP as your mail provider.