What is the Google-recommended SPF setting for a domain that uses Google Workspace as the primary mail system?

The recommended SPF setting for a domain that uses Google Workspace as its primary email system is to choose the "Reject" option. Setting your SPF record to reject emails that fail the SPF check provides a higher level of security against spoofing and phishing attacks. This means that if an email is sent from a server that is not authorized in the domain’s SPF record, it will be outright rejected by the receiving mail server, preventing potential fraudulent messages from reaching users' inboxes.

This approach is part of a broader set of email authentication measures, including DKIM and DMARC, that help ensure the integrity and authenticity of the emails sent from your domain. By implementing a rejection policy, you actively safeguard your domain's reputation and enhance the trustworthiness of your email communications.

Other options like "Deliver with modification," "Quarantine," and "Pass" are less secure and may allow potentially harmful emails to reach users, either by modifying them, putting them in a spam folder where users may still access them, or passing through completely without verification. Therefore, rejecting non-compliant emails is the most responsible approach when configuring your SPF settings for domains using Google Workspace.