Calendar feature is sorely missing though it seems this service also doesn't have it. I guess calendar is a pain to set up/troubleshoot timezone issues, etc
The killer features are unlimited mailboxes and per-mailbox quotas. I make a new mailbox for every device and give them a quota that makes sense; 10 messages per day for most. If a device goes haywire, gets compromised, or gets stolen, it’s one mailbox to fix and maxes out at a super low quota, so it’s useless for spamming.
That’s 100x better than the options on Office 365 which absolutely sucks ($$$) for low volume email coming from devices.
(It's been three years since I tried it, and looking at my notes, I couldn't get Zoho to sync contacts for me, and somehow didn't get calendar notifications.)
The biggest annoyance is that someone used mx, mx2, mx3 for their MX instead of mx1, mx2, mx3, so the dns record indentation doesn’t line up. Lmao.