Only few percent of emails are actualy delivered to my Inbox

Only few percent of emails are actualy delivered to my Inbox

Before using Zoho email services i was using other email service provider , there i receives too many email on daily basis (of course most of those were spams ) but still i was receiving each and every email ... but after getting zoho email services I developed a feeling that i am not getting all of the emails ... same was later confirmed when many of my vendors reported to have sent me emails BUT i was`nt getting those emails...
So tell me...what might be the problem  ? or is that as i am currently using your "Free" subscription .. that has all these issues/problems ?