I had a good backup but I found out that if I imported the rules-backup, the original rules were not replaced but instead the imported rules were added to the list. So you need to remove all all the rules by hand first and then import the backup. My Outlook contains more than 100 rules and I had to delete and confirm them all one by one. There is no setting in Outlook that lets you remove all rules at once.
Fortunately I found the following website which show a commandline switch to start Outlook and remove all rules:
Start > Run > outlook /cleanrules
I found out there are a lot commandline switches to start Outlook:
This isn't Excel related at all but I found it interesting enough to share.