I was trying to use some Outlook 2013 plugins to help sort e-mail, and came across a bug where the location of e-mails in Outlook 2013 get out of sync with there location on the server (e.g. by viewing via the Zimbra web client).
I managed to trace the problem to when Outlook sends a create folder and move e-mail operation in the same activesync operation, and have found a way of replicating thisjust using Outlook alone (thus ruling out any problems with the plugins themselves)
This is using Outlook 2013 running on Windows 10, syncing with Zimbra 8.6.0_GA_1153.FOSS using ZSuite 2.0.4. However, I can also replicate this in Outlook 2016 on Windows 10, and Outlook 2013 on Windows 8.1.
Start Outlook 2013 (connecting with Zimbra via ActiveSync).
In the Send/Receive tab, click on Work Offline and verify it says working offline in the status bar (alternatively disconnect the computer from the network).
Create a new sub folder under Inbox
Move 2-3 e-mails from Inbox to the new subfolder
Click again on Work Offline in the Send / Receive tab and verify that Outlook is now connected in the status bar
Check the account via the web client (or Zimbra Desktop)
You will find that whilst in Outlook you have the new folder with 2-3 e-mail present, in the web client (or Zimbra Desktop) the folder is also present but is empty, and the e-mails are still in the inbox.
Matthew