Several users in the company want Zimbra emails to come through on iPhone, and use Outlook. On iOS, they set up email using Exchange method. When Outlook is used, emails get removed from Zimbra side once synced up, helps so quota doesn't get reached. This also helps with saving a permanent copy on Outlook side locally in PST. (If there's a more sensible way, I'm open for another solution)
It was working ok up until now. When new message comes in, you can see it in iOS, but when Outlook syncs mail, it removes it from Zimbra side, but it sticks around on iOS Mail app. If you try to delete the message it gives the error:
Unable to Move Message
The message could not be moved to the mailbox Trash.
In other words, Mail app doesn't refresh properly, so you end up with new emails just piling up. I've tried readding the Exchange way, turning account off and on as well. Could look into IMAP or POP perhaps, but it's a pain for users using Exchange way along with Outlook on PC. Not sure why it broke.
Zimbra version: 8.5.1, iOS version: 8.1