I broke Kmail after upgrade to 4.9.2

[Thiudans]

This is my fault, BTW. The upgrade went smoothly but I tried to fix a minor error.

So, I upgraded and I was getting an annoying, though minor, error message. While fiddling around, I deleted an IMAP folder within Kmail on my Gmail account--I received a warning and deleted the folder; foolishly as it turns out.

After that, I cannot download any gmail emails and I get the following error:

"Unable to append item flags"

OK, so I apt-get remove --purge kmail && apt-get install kmail and try again--same error. I also noticed my user account information was intact; however, I think that is the problem, something is corrupted in my user account settings.

I tried to set up my live.com email, but I get an error saying it is an unknown collection.

I was contemplating removing kontact, but I would really just like to purge the settings to it is "out of the box." Is this possible?

[SteveRiley]

Log out of KDE. When you see the login screen, press [Ctrl]+[Alt]+F2 to switch to a TTY console. Log in with your regular user ID and password. Then:

rm -rfv ~/.kde/share/apps/kmail2/
rm -rfv ~/.kde/share/config/kmail*
rm -rfv ~/.local/share/akonadi/
rm -rfv ~/.config/akonadi/
rm -rfv ~/.kde/share/config/akonadi*

Logout. Press [Ctrl]+[Alt]+F7, which brings you to the graphical login manager. Log in. The commence reconfiguring KMail.

[Thiudans]

SetveReily,

That did it! Everything works.

Thanks!

[SteveRiley]

My pleasure. Glad it's working for you.

[Guest]

Log out of KDE. When you see the login screen, press [Ctrl]+[Alt]+F2 to switch to a TTY console. Log in with your regular user ID and password. Then:

rm -rfv ~/.kde/share/apps/kmail2/
rm -rfv ~/.kde/share/config/kmail*
rm -rfv ~/.local/share/akonadi/
rm -rfv ~/.config/akonadi/
rm -rfv ~/.kde/share/config/akonadi*

Logout. Press [Ctrl]+[Alt]+F7, which brings you to the graphical login manager. Log in. The commence reconfiguring KMail.

This hint totally saved my backside!
I did not find a way to use kmail on Debian Jessie, and even tried to change my mail client after... don't know, 10 years? - but now I could get back.
Although this thread is old:
Thank you very much!

Addendum: Oops, it seems this has deleted all my knotes content. (But then, it was kind of an eternal write-only note.)
Handle with care...

Ciao,
Eike