After sending out hundreds of client emails through ZoHo Mail, and after receiving several phone calls that emails have been sent that I have never received.. am I correct in assuming that Sales Inbox is not an option going forward?

Why would there not be prompts preventing you from being able to send emails if it's never going to actually sync with my email inbox. 

I cannot begin to wrap my  mind around how much this mistake could potentially have cost me if those emails are not findable...