How to get every email to/from a lead or potential to display?

I'm newer to Zoho, so maybe I'm missing something obvious to more seasoned users, but here's my situation and questions:

Setup: I've set up my Zoho CRM to pull emails in through our Gmail into the Zoho app, so I'm creating/replying through that feature now.
Leads/Potentials (my problem): When I get a new lead (let's say someone calls)... I go to leads, set up the lead, and then create a potential. I can send an email to the contact from the Leads, Potentials, or Contacts screens, but I can't seem to get any of their replies, or my replies, to stack/appear in with the list of other emails I have sent. It's as if they come into the system and never get recognized as belonging with the lead/potential/contact, etc. as appropriate.

So, I either have to copy/paste the email content from their reply into an email I create from under the "Leads" or "Potentials" section (then paste that info under the signature block so there's a thread to follow), or I am stuck replying in the email client itself (through Zoho), but it never gets linked back to the lead. I've tried the BCC Dropbox feature, but that doesn't seem to work, either.

What am I missing???