This app's main purpose is to delete e-mails directly on the server without having to download them to your computer first. This is useful, for example, if you want to nuke a bunch of spam without downloading it and letting your mail client's filters deal with it, or getting rid of huge unwanted attachments that are clogging up the inbox on your mail server.
This kind of app was more useful back when everybody's connection speeds were slower (e.g. 56K modems), bandwidth was limited, and download limits were much smaller (measured in MB rather than GB). However, it still has its uses. For example, I often work in remote worksites that only have slow dial-up or cell connections. If someone sent me a 20 MB video via e-mail, not only would it tie up the line all day, but I wouldn't be able to get my other e-mail until it was finished downloading. Using an app like MyPopBarrier, I can delete the big attachment on the server and save time, download capacity, and connection charges.
Note: I have no association with the author of this app. In fact, I don't even use MyPopBarrier! (I use a competitor's product :-) ). Just wanted to clear up any confusion about apps of this nature.
(Version 2.6.1)