Mail doesn't reach destination: ZOHO mail IP is listed as a SPAM !

Mail doesn't reach destination: ZOHO mail IP is listed as a SPAM !

Hello, the problem is that mails we are sending to one of clients doesn't appear in their mail system.

Is it possible to track the routes and find where the problem is?

Thanks.

UPDATE:

ZOHO mail IP is listed as a SPAM !

Zoho, please fix this problem immediately!