View Zoho Mail through CRM as Web tab

View Zoho Mail through CRM as Web tab

I'm really struggling to get my sales reps to move from their gmail to zoho mail. I think one way I can do this is if they can view their email from within Zoho CRM.

So I tried to create a webtab with mail.zoho.in but it cannot display? I did some research and it seems they don't let Mail be framed, but surely to allow it within CRM would be a really easy and simple way to provide a seamless mail/CRM experience?

In fact, it would be great to be able to do this with all the Workplace apps!