I haven't had any problems with outbound deliverability. However, their inbound post-delivery spam controls are overzealous and categorize almost all mail from new correspondents as spam.
The only major problem with Zoho is that they host mail inside US jurisdiction so it's vulnerable to NSA abuses.
Mailbox.org (based in Germany) is a possible alternative for people who want/need to keep their data further away from American commercial espionage operations.
I was aware that my zoho mail is hosted in the U S. I did originally look at mailbox.org as well as as posteo and another European based provider but can't recall why I had discounted them. (None seemed horrible or anything like that; just zoho won it by minor margin.) The beauty of having my own domain is that if I'm unhappy, I can switch later on.