SPF tells receiving mail systems which servers are authorized to send mail for a domain. DKIM adds a cryptographic signature to messages so receivers can verify that the content was signed by an authorized system.
What to consider
DMARC builds on SPF and DKIM by publishing a policy and providing reporting about messages that use your domain. It can help reduce domain spoofing when configured correctly.
Roll out DMARC carefully. Start with reporting, review legitimate senders, make sure SPF and DKIM alignment is correct, and only then move toward stronger enforcement.