<p>I use IMAP access to my accounts mostly to train the server's spam filters and message archiving. It works as advertised. Today I was selecting a bunch of messages with the only intent to mark them as READ and noticed it was taking too long to mark the UNREAD messages. Usually, I use rules for this kind of job but some mail servers (Gmail) do not cope well with rules and I don't have the slightest idea why. Yahoo and GMX do just fine.</p><p>Anyway, this particular IMAP folder has 7.1% of UNREAD messages and the rest marked READ (92.9%). I think I can fairly assume Pmail will run over the whole messages at least ONCE, that is, to build the header cache. The time taken for this task was 5' 25". Differences between the three measurements were considered irrelevant. The problem is that the existence of a header cache, or not, does not influence on the selecting messages time. Pmail was still downloading all the folder's messages before comparing. Is that correct? I was expecting that only those message headers not already on cache should be worth downloading.</p><p>I'll be eagerly waiting for your thoughts. TIA. </p>