What SPF, DKIM and DMARC do
SPF
SPF lists the servers allowed to send email for your domain.
DKIM
DKIM adds a digital signature to help receiving servers confirm that mail has not been altered.
DMARC
DMARC tells receiving servers what to do when SPF or DKIM checks fail.
Why they matter
Correct email authentication can improve deliverability and reduce spoofing of your domain.