SPF is short for sender policy framework. it helps to assign mail servers that are allowed to send emails via your domain. in other words, it helps to prevent people from sending emails through your domain. emails not included in the SPF will be automatically sent to the spam folder or rejected totally. This is just a requirement by email clients like Gmail, yahoo, outlook, and Hotmail for email senders to protect their clients who are normal Gmail users from spam and unsolicited emails.