As a consequence I am also unable to view any comments to the admin user....

Thank you for reporting. We'll check these issues in the morning.

Ok, these notices will be fixed in the next release (this week).

The fact that the emails don't arrive is a different issue that takes out outside of b2evolution.

http://b2evolution.net/man/email-notifications-don-t-work

As an email client I use Thunderbird.

On an global search with b2evolution not any mail is present in any of the accounts or folders,containing over 2.5Gb of data.
Previous activation requests did arrive as expected, as does yours currently.
My mailprovider is one of the biggest in the Netherlands and I do receive plenty of other mails.
I checked via webmail wether there was ony mail residing in any of the remote folders
This was not the case.

I did the same for the other provider, as messages might have been sent to the wrongly entered mail address at first.
This is not the case.

I am pretty sure mails have not been sent by b2evo, though I cannot check that as I have no acces to the account at all

BTW, is there an uninstall funcion other than complety remove the application code and the database to start from scratch?

The bugs you mentioned were fixed in v6.6.0.

Lost password recovery, even if email doesn't work: http://b2evolution.net/man/lost-password

Enable installer option to delete DB: http://b2evolution.net/man/basic-config-php