Read / Unread Status not Syncing with the Server
If your read/unread status is not syncing with the server, try these settings:
1) Preferences or Options / Accounts / [your account] / Advanced Button
* Uncheck "Use Idle Command"
* Set Max Server Connections To Cache = 1 (default is 5)
2) Then go to: Preferences or Options / Advanced / General / Config Editor
Paste the following into the Filter field:
And double-click it to change the status to False.
3) Restart Postbox.