The Apple Mail VIP Feature: VIP Entry for One Person With Multiple Emails
The Apple Mail VIP feature has been convenient, saving me the trouble of making sets of rules to organize my mail.
But the Apple Mail VIP feature became problematic for one simple reason: my contacts often use two or even three or four emails, leading to that many entries for the same person.
For a solution, see Apple Mail VIP Feature: Multiple Emails for one Contact.