IMAP undeletable mail

[mtk]

Hi,

I sometimes have an issue where an email that has been marked read or even deleted in the Zimbra Web Interface (Zimbra 9.0.0_GA_4028), persists being unread or in the inbox through IMAP. No matter what mail client.
It is not possible to mark it read or delete it thorugh IMAP, it will keep popping back.

So, for some reason there seems to be an information gap between IMAP and Zimbra Webmail. Anyone has a clue how to resolve this? I already tried re-indexing the mailbox.

Thanks in advance!