Comment 139 for bug 883459

András, I'll have a look at the sources, but I fear the KMail/Akonadi codebase is a bit too hard for me (I have not been into the C++/Qt business very long yet ;-). But I'll try.

Another thing to substantiate the suspicion that the duplication does not happen when the mails are filtered but when they are delivered:

Yesterday, I saw that the default setting for filtering when selecting "Filter incoming messages" is that all "Accounts" are used for filtering. This includes not only the POP3 accounts (which are actual ones), but also the local maildir "Accounts".

I selected only my POP3 account and deselected everything else. I also deactivated my "/usr/bin/sleep 0.3" hack filter. After that, I ended up with filtered mails being written to their respective target directory and a (physical!) copy of those very mails being written to my inbox.

So it's actually the case that the emails are simply delivered twice, one by the filter agent and one by the, (?) pop3 agent, and the duplicating really happens because the inbox notifies new mails and the filter agent is invoked again.

Perhaps, this is "only" a sequence problem and the filter agent is invoked too early?! Can anybody who's into the code base right now check that? Otherwise, I fear we have a design problem here :-(