[Dovecot] Outlook 2003 and Thunderbird IMAP + getting new headers

Hi,

We run 1.1.3 and I use Outlook to connect to my IMAP box and a couple of times per day (randomly) when I click certain folders IMAP will start retrieving ALL headers for that folder again ('retrieving new headers')!

I don't understand this. What triggers IMAP to do so, why not just retrieve only the NEW headers?

Is it Dovecot or Outlook (probably) and what can be done about this? I already use the Dovecot Outlook workarounds.

I have also gotten word that this behavior happens with Thunderbird.

This is really a problem causing a lot of load on our storage (I am not the only user).

Cheers,

Jan