DMARC compliance via DKIM. Contact Mixpanel Support for guidance.
Relay email through your own SMTP server to get DKIM into place. Contact Mixpanel support for configuration guidance.
Note that Mixpanel's documentation suggests adding include:datadrivenemail.com to SPF records. This does nothing as Mixpanel uses its own domain (datadrivenemail.com) in the context of SPF.