DKIM (domain keys identified mail) which is a method to validate the authenticity of email messages.
SPF (Sender Policy Framework)
Why need to verify DKIM and SPF in our platform?
you're telling recipients that you've authorized Marketo to send emails on your behalf
Without this change, your email has a higher chance of being marked as spam since the email was addressed from your domain but was sent from an IP address with a Marketo domain.