cur, new, tmp folders in local mail folders

HI

How do emails get dealt with by kmail2? Do unread emails wait in "new" and 
when read they get transferred to "cur"? If i use dolphin and look into these 
folders i find old emails still in the "new" folder.
The old "Retrieving folder..." message is persistent on one of my folders then 
spreads to all the others after that. I've tried akonadictl fsck/vacuum loads 
of times and sometimes it fixes the issue .

Regards

Ian

-- 
opensuse:tumbleweed:20170129
Qt: 5.7.1
KDE Frameworks: 5.29.0
KDE Plasma: 5.8.5
kwin5-5.8.5-1.1.x86_64
kmail2 5.4.1
Kernel:  4.9.5-1-default
Nouveau:  1.0.13_2.2