email inaccessible through imap after reading

[Martin Kraus]

Hello.
  I'm having problem with emails being inaccessible through imap after reading
it in outlook. The email file is still in the INBOX if I grep for it's mail id, but no
imap client displays it. I've tried with mutt and pop3  but I couldn't find the 
email either.

This server uses cyrus 2.3.14. I've never had any similar problems on any of
my other servers. My guess is that outlook does something to the message to
hide it from displaying but I've got no idea how to check this.

Does anyone have any idea why would this happen?

Thanks
Martin Kraus