Ensenta supports DMARC compliance via SPF.
Contact Ensenta to ask about DKIM capabilities.
Traffic seems to come only from 'monitor.ensenta.com', the address of which for the moment is '153.69.200.104'. Given that information, you could either add 'a:monitor.ensenta.com' to your SPF (which would use 1 DNS lookup, but would account for a change of IP) or you could add 'ip4:153.69.200.104' (which won't use a DNS lookup but bears the risk of Ensenta switching the IP and your emails failing). Either way, it's best to contact Ensenta and verify this information before making changes.