Check the passwd file, the home of the usre otrs must be /var/lib/otrs (or better: the current directoty hosting otrs stuff).
Remove the .dist extensions from crontab templates. Run Cron.sh
Grab incoming mails via fetchmail. Run fetchmail as a daemon.
/etc/fetchmailrc shouls contain
poll imap.mailserver.de protocol IMAP user otrsmailuser password otrsmailuserpassword ssl is otrs
Using RADIUS:
Check '''defaults.pm'''
# This is example configuration to auth. agents against a radius server
$Self->{'AuthModule'} = 'Kernel::System::Auth::Radius';
$Self->{'AuthModule::Radius::Host'} = 'radiushost';
$Self->{'AuthModule::Radius::Password'} = 'radiussecret';