My emails occasionally go into recipient's trash or spam account

My emails occasionally go into recipient's trash or spam account

I have repeatedly had my emails sent to the trash or spam mailboxes of the person I'm emailing, including individuals who had successfully received them earlier. This seems to make no sense, but only happens with my Zoho email, not my other providers. And it keeps happening, which means I don't really know if the intended recipient has actually received what I sent them. Any fixes for this?