How to setup SPF records / DKIM sender ID in Zoho Campaigns
Please follow the below link which explains on how to setup SPF and DKIM records to your domain's DNS settings.
The settings are provided in Zoho Campaigns under
> Settings > Senders > Setup (SPF/DKIM)
From there you can copy the codes and update them in your domain. The above link explains how to do this in various hosting providers like GoDaddy, HostGator etc.