What is SPF or Sender Policy Framework? SPF is a type of DNS (Domain Name Service) record that specifies what email services provers can send email on behalf of your business domain.
Example: your business domain, mybusiness.ca uses Microsoft Exchange Online AND a newsletter service. You need a DNS record to authenticate Microsoft Exchange and the newsletter service can send on behalf of your domain. Receiving email servers check your DNS records to see if the sender is authenticated or spam. See example below
SPF is part of the holy trinity of email authentication: SPF, DKIM and DMARC. See What is DMARC, DKIM and SPF Email Authentication for more details.