To authorize Rare Vantage to send emails on your behalf you will have to include it in your SPF record. The SPF record mechanism used by Rare Vantage is shown below.
To enable DKIM you will have to reach out to Rare Recruitment support team who will provide you with the necessary TXT record to create in your DNS. Once created, please let them know and they will enable the DKIM signing process for you.
Create a free OnDMARC account to test your configuration.