The Zoho mail app is relatively solid. It's no Outlook or Gmail, but if that's the tradeoff for a little privacy, no problem. 

The calendar app, though... yikes. It's not ok at all. I get alerts for events that are hours off (or happened yesterday) or for events that are deleted. It has absolutely no ability to interpret time zones. Etc. 

Has anyone integrated a different calendar app with their mail?

Matt