How do I stop Outlook 2016 from applying rules to multiple folders?

Question

Somehow Outlook started applying rules to two completely different e-mail account folders (see screenshot). This results in rules made for e-mail address 1 being applied to messages received on e-mail address 2. As you can see, the drop-down shows a separate entry for account 3.

Why did Outlook link account 1 and 2 together and how I can split them?

Answer 1

I ended up removing all accounts from Outlook and putting them back in but that didn't help. Eventually I added the 'through the specified account' constraint to all of my rules. Dirty workaround but at least my mail doesn't get mixed up anymore.