Martin Meredith asks if mail should be filtered on the imap-server or on the mail client side. The answer in my humble opinion is both.

First of all you want to be able to filter things on the server side, for me that means splitting the KDE stuff from the work and private mail.

But after that I can still imagen you want to do spamassassin on your computer if the hoster does not provide it for example.

The trick in all this is that it should be easy for the user. That means that the server side filters should be configurable inside the application, just like where you setup regular filters. Maybe in an ideal world it is just a combined view to the user, possibly just a checkbox ‘Apply this filter on the server’ if needed.

There exists a sieve library within KDE, I haven’t looked at it yet, but it is on my list to look at, it would be nice to have full support for the server based sieve filters within any KDE application that wants it. But it is not on my short-term todo list. And I would be very happy if someone else beats me to it.