Hi., I found some bug in your website, I will describe in two scenarios,

case 1 : 

Initially, I disable running JavaScript in my browser for all webpages. Now, I try to login in ' https://www.zoho.com/mail/login.html' it show some warning message say "Note : JavaScript is disabled in your browser. Please enable the JavaScript to continue.", this is working fine. but when I try to login with the link ' https://mail.zoho.com' it doesn't show anything to me, it just show only the blank page. Actually, it must to say at least some warning messages. 

case 2 :  

On the another hand, after successful login I can able to see everything is fine. Now I disable running JavaScript in my browser. And reload the page, same thing happens again, it doesn't show any warning or error message, it simply shows loading symbol.... for a long time.... 

My suggestion : 

When I check your HTML code, just right click on the webpage (view source code) option, it says to me there is no HTML tag called "<noscript></noscript>". Please handle this functionality. And say some error messages or warning messages link in gmail,Facebook etc.,

Platforms : 

OS : Windows 8.1

Browser : Google chrome