Gmail marks mail coming from Zoho as "Unable to verify that [mydomain.com] actually sent this message (and not a spammer).

Gmail marks mail coming from Zoho as "Unable to verify that [mydomain.com] actually sent this message (and not a spammer).

Gmail recently started marking emails coming from my Zoho account as "Unable to verify that [mydomain.com] actually sent this message (and not a spammer)."

Gmail links to this page to learn more. https://support.google.com/mail/answer/180707?hl=en

After reading about DKIM, I found a guide for setting up DKIM and SPM for my domain at GoDaddy. But this required me to set up of Zoho Campaigns to do this.
https://www.zoho.com/campaigns/help/setup-spf-dkim.html

So far, this hasn't fixed the problem. Is there a more appropriate way to generate and setup a DKIM and SPM for Zoho Mail specifically?

Thank you,