The mixedmaildir resource looks like a really good idea, but...

To scan an mbox file with 6000 emails after 1 new mail has been added, mutt needs less than 1 second for a complete and accurate scan, and that without any kind of index caching or any other bloat at all. kmail needs 10s of seconds to 5 minutes!!!! And that will all that phenomenal SQL bloat hanging off it - or perhaps that's the real problem.

A complete restart of akonadi and kmail will be necessary when selecting different folders and an email in each of them without making sure first that the previously selected 
Frequently kmail gets stuck "synchronising" altogether. The only recourse is to quit kmail, stop akonadi, wait for akonadi to exit (a minute is easily possible - dang it's tempting to use kill), and start again. But then it could be it's not a deadlock - difficult to tell how many hours to wait for a miraculous recovery, with tens of folders times 5 minutes.


Reproducible: Always

Steps to Reproduce:
1. Create a mixedmaildir resource for an existing directory with subdirectories, all containing only mbox files.
2. Try to get some work done: append an email with another program + with kmail, resync directories incl content because kmail's state isn't accurate or uptodate, select a folder and an email within, then select another folder and an email within that before the first one finished doing anything useful to the user (like show the selected email), ...
3.
Actual Results:  
Unusably slow perofrmance, deadlocks.

Expected Results:  
Speedy performance on modern hardware.