kmail2, exim and /var/mail/$user locking

[Matthias Großmann <grossmms@googlemail.com>]

Hi,

most of my mail is delivered to /var/mail/matthias by exim, and I'm using 
kmail to read it. This worked pretty much out of the box with Wheezy. After 
upgrading to Jessie, I created an extra receiving account for 
/var/mail/matthias, which is causing problems: Mails, which I already did read 
or even delete occasionally show up as new and kmail sometimes fails to 
compact the mbox file.

I assume this happens because kmail does not lock /var/mail/matthias, but I am 
a little bit confused about the locking methods. Exim supports "fcntl", "flock" 
and "lockfile", while kmail - according to its help pages - supports "procmail 
lock file", two variants of "mutt dotlock", "fcntl" (default) and none 
(discouraged). The setup dialog, however, does not contain an option for 
"fcntl", and defaults to none.

So I'm wondering what the recommended configuration for my setup would be.

TIA,
 Matthias