SPF
Adding SPF for Brevo (formerly Sendinblue) for DMARC purposes is not needed because the Return-Path address of the emails is set to their default domain in order to track bounces on your behalf. Therefore, SPF will not pass for Brevo from a DMARC perspective, however, as long as DKIM passes, the emails will be DMARC compliant.
DKIM
To enable DKIM you will have to create a few DNS records. Please follow the instructions using the button below for more information.