Kmail2 does not save the state of the folder tree, e.g. which parts of the structure were expanded or collapsed. After startup all servers are collapsed and if you have folders nested in several levels, it takes you quite a while to get the your mails. If you have a several hundred folders and levels, restoring the previous view is quite a bit of work - if not impossible. This is a serious regression compared to the old kmail. Data loss is usually considered a major issue in bugzilla and since the state of the folder tree is kind of data - at least configuration - , too, I am setting the severity of this bug accordingly.
This issue is also a problem for my personal workflow
I increase time when we restore it. Now we have 60 seconds and not 10 seconds. So I hope that it will fix it (need kdelibs 4.9)
Reopen it if necessary