Emailing out of CRM and having reply come back

We have having issues at times when we email a client out of ZOHO CRM … client responds but does not always go back into the email section of the account.

Is it possible you have different email options setup on the send button?
Multiple email setup for 1 person… But I still think it should show up.

Are you using Zoho Mail or a 3rd party provider and syncing it?
Did you tell support?