I've used Pegasus Mail for the last 12 years. I love it for the filtering capabilities because there are so many ways to filter and manage e-mail with it. With the filters setup correctly I don't have to read through junk mail, and my wanted mail arrives in my In Box.
I use Pegasus to sort my mail, sort my folders, color code my incoming mail based on what it is, and sooooo much more.
For example, if I let my legit mail accumulate in my In Box I simply make a few clicks and a filter sorts the mail and deposits it into mail folders with the names of the various senders. This is handy when I have a gazillion accumulated emails from Jim, Joan, Nancy, George, Greg, Julie, etc. A few clicks and I can file 5 different people, or 50 different people. Or I can set it to file them automatically each time I close the New Mail folder.
Lets say that I've created a Sketchup file I'm willing to share with folks. To receive the file I instruct them to send me an email with Send Sketchup File in the subject line. When an e-mail comes in with Send Sketchup File as the subject, Pegasus Mail processes that message, creates a reply with the file attached and sends it, then files the incoming and outgoing emails into a specifed folder. This is done with no intervention by me.
And it does lots more......