MAIL CLIENT ONLY

I've read several threads already but still haven't found out whether I can just use ZOHO as a client interface without having to migrate my hosting to them. I have my own mail server and host all my domains for security reasons. I just want to use ZOHO's GUI (client) to simplify integration to their CRM software back and forth. Can anyone tell me if this is possible since I can't get anyone from Tech support on the phone or get a reply by directly emailing support.