I've migrated a few accounts into Zoho. That is, I've created a new account in Zoho and used the Zoho migration tools to bring emails across from the old account. The mails seem to have come across correctly. I can see them online, using mobile clients mapped via IMAP, on iOS devices using ActiveSync and using Andorid's native email application using ActiveSync.
When I use CloudMagic using ActiveSync, I get a generic server error ("The server encoutered an error. Please try again later.") with no way to get additional details. But, I only get this when I try to fetch emails that were migrated. Emails sent directly to my Zoho accounts work fine.
Is there something about the way that emails are migrated that would impact some implementations of ActiveSync but not all? I have an incident open with CloudMagic as well. It sure sounds like both sides are culpable on this one.