I have experienced the same problems. I have tested the emails that I receive on many different PCs at several locations. Mail that gets received takes 5 minute up to 1 hour (Sometimes even more) I have discussed this with Aron in their tech department and he basically blamed everything on my server my pc my email account. However my emails get to me almost instantly with other email clients. (I have tested side by side).
ZOHO....You need to look into getting this fixed and not pushing down the road. It is a real problem that needs to be fixed yesterday. As I explained to Aron, I ran a ping test (that was set up by my email server) and they found that there is a server that is being used by ZOHO that is causing the problem.
It is not you customers fault or their place to help you fix your problems.
I hope you get the issue resolved so we can resume using ZOHO MAIL. All others looking to use ZOHO Mail, I would urge you not to until actual customers say the problems are resolved.