POPFile

POPFile is an email utility that enables you to setup a system to automatically sort out important messages from junk, spam and advertisements.

It does not have an interface of its own

It is necessary to mention that the utility does not include a standalone GUI and it opens in your default browser from where you can access 6 main tabs. On a side note, you can change their looks and display by accessing the Configuration tab.
While at first it does not seem to do or display anything, do not fret. Since the application is designed to work on the specifications you provide it, it requires you to configure it first. More exactly, you need to specify the criteria (Buckets and Magnets) the app should watch out for.

It can be a simple tool for the average use

It is necessary to mention that the program can be set to perform a simple job, namely sort out junk emails. In this case, you simply define the categories to watch out for using specific keywords and the app sorts messages automatically.
In addition, you can use the quarantine function to get an idea about the contents of suspicious emails without having to open any attachments.

It can act as an all-inclusive utility

POPFile's functionality can be extended to creating virtual mail folders where emails are processed more minutely. As you already guessed, properly configuring the app to sort out emails in this case implies altering parameters and variables, so it addresses to advanced users mostly.
Regardless of how you choose to use the program, you should know that it does not automatically delete emails. In fact, even messages containing your criteria are just filtered and sent to a specific mail  folder.

Can be useful for users using multiple email clients

While it does require you to make separate configurations for each one, POPFile can be useful when using multiple email clients and need to quickly identify the important message within hundreds of messages you receive daily.