When I used Zoho Free, many of my emails would end up in people's spam folders. My domain is certainly not on any blacklist, it was pointed correctly and with the security and domain validation features enabled and everything configured properly. Deployed it to small business clients as well and same result.
Gmail doesn't seem to like Zoho.
What seemed to work like a charm was to use iCloud+ Custom Email and just add my custom domain addresses as aliases on Gmail. It's like having a custom domain Google Workspace without paying anything (apart from the iCloud subscription that gives you a ton of space for all your data).
/mediastack. Has all my movies, shows, music, books, audiobooks etc.