To authorize Jangomail to send emails on your behalf you will have to add the below SPF mechanism to your SPF record in DNS.

include:jangomail.com

For more information on configuring SPF with Jangomail please click on the button below. 

Jangomail also supports DKIM signing. Please click on the button below for information on how to enable DKIM signing in Jangomail. The page also contains a video demonstration. 

Create a free OnDMARC account to test your configuration.