SPF is a standard email authentication method. SPF helps protect your domain against spoofing, and helps prevent your outgoing messages from being marked as spam by receiving servers. SPF specifies the mail servers that are allowed to send email for your domain. Receiving mail servers use SPF to verify that incoming messages that appear to come from your domain were sent by servers authorized by you.
Without SPF, messages sent from your organization or domain are more likely to be marked as spam by receiving mail servers.
In addition to SPF, we recommend that you set up DKIM and DMARC. These authentication methods provide more security for your domain, and help ensure messages from your domain are delivered as expected.