1) How do I close my account?
2) How do I delete my account's primary eMail address?
3) How do I delete all my posted messages?

On the bottom of each forum page:
"All messages belong to and are the opinion of their respective authors."

I want to delete my property ("messages belong to…authors").

How do I get a legally valid confirmation, that all
my data is really destroyed and no copies exist on
Your backup servers, or Your partners services/servers?

Are there other Terms and Conditions in place,
which contradict "messages belong to…authors"?

Are European data protection laws in force?
Or do You have an exception, somehow?

Ask the Forum admins by PM.

Just to put some balance: the offender was banned, no need to leave. It is usually a way better reaction to actually report offenders rather than leaving yourself.

We are not very keen on deleting messages that are part of discussions, but of course this can be done. Please write this in your message to the forum administrators.

Thanks for Your answer.
I got a friendly answer from a KDE Sysadmin.
I sent my answer.

Therein, I explained why it would be best for me to cancel
my forum membership.

Thanks again.

This is a nice forum and KDE is great.
You and Your team/project members are all honourable people.

Nonetheless, I will leave.