To authorize Blackpearlmail to send emails on your behalf you will have to add it to your SPF record. The SPF record mechanism used by Blackpearlmail is shown below.
For more information on SPF please click on the button below.
Blackpearlmail also support DKIM signing for your custom domain. They can either provide you with TXT records or CNAME records. You will have to reach out to their support team and request for them to DKIM sign your emails and they will provide you with the necessary records that need to be created in DNS for your domain.
Create a free OnDMARC account to test your configuration.