To allow Atmail to send emails on your behalf, you will have to add them to your SPF record. The SPF mechanism used by Atmail is shown below.
Europe server: eu-spf.atmailcloud.com
USA server: us-spf.atmailcloud.com
You can configure DKIM support through Atmail. To learn more please see the button below.
Create a free OnDMARC account to test your configuration.