I've had clients say they haven't received emails from me with important contracts etc, then I check my sent mail and it's not there but I know 110% I sent it. It might be when I attach a document as that seems to be a trend? 

We pay for various Zoho services, so I'm hoping someone can help me out here?

I use exchange setup on my iPhone and works a charm, can we not setup exchange in mac mail or outlook for mac? 

thanks