Happy to be be proven wrong as I haven't used this specific service, but the quality of Zoho mail-related offerings is so laughingly bad that I wouldn't touch any of their other products.
I use Zoho CRM. it's actually pretty good in terms of customization reliability and features. I used to maintain a SugarCRM CE instance for several years after they stop supporting the community edition.I Could no longer afford to spend the time to maintain it so I replaced it with ZohoCRM.
You're right about their Mail solutions though they're not that great.
