Fine-tune our company's instance of Zoho Mail

Our company is a user of Zoho One (suite), which includes Zoho Mail among the many other Zoho apps we have integrated into our process. But our Zoho Mail constantly sends (30%+) good emails to spam. We have tried to reduce the amount of emails going to spam by adding email addresses and domains to the Zoho Mail Admin Console/Security and Compliance/Spam Control's list of Allowed and Trusted lists of trusted email addresses and trusted domains--and still they to to spam. We mark the good emails in spam as "Mark as not spam" and the emails then go to the Inbox as they should, only to quickly revert back to the spam folder. We are seeking someone who knows how to work and fine-tune Zoho Mail and get this working right.