Our data indicates ActiveTrail is DMARC compliant via both SPF and DKIM. Check their site for further guidance: https://www.activetrail.com/email_marketing_software/learning/guides/how-to-authenticate-your-email-account
Contact ActiveTrail support for DKIM setup.
ActiveTrail provides the following include - 'include:_spf.activetrail.com'. Make certain that this sender is configured to use your domain before you add the SPF record to your domain.