There is a wonderful feature in Outlook (PC or Mac). You can ignore all emails by conversation or email alias. There are 5 people in my current organisation that my inbox rules routinely place in a special folder… a folder I rarely look at… and my life is better for it.
Today, however, marks a new first.. I now routinely screen all mails to a special folder from one whole business department. The constant and thoughtless communications from this lot have been getting in the way of the day job… so marked with the Black Spot they be.