I disagree with both responses provided at this point because there are ways within BoxTrapper to mitigate backscatter SPAM. Note, that the SPAM referenced here are the "Challenge" notifications sent by Box Trapper to authorize the release of pending e-mails.
I don't know of any major cPanel hosting company that enables Box Trapper by default. It's considered more of a power user tool. That said, I have been using BT for almost 10 years and I love it. I'll admit the software was a bit of a resource hog back in 2004 - 2007 but it has been optimized somewhat and servers have become much more powerful in that time frame. Today, it should not be an issue for any but the crappiest servers or the most inexperienced admins.
While BT can challenge every e-mail, the default is to always allow e-mail from individuals who have been successfully challenged previously. Besides white listing, the software makes it super easy to utilize Ignore Lists and Black Lists (neither of which will result in any further communication from your server).
Anyone who has the technical ability to read the full headers of an e-mail can discern where mail is really coming from and block not only individuals but entire domains - i.e.,
BT, used in conjunction with Spam Assassin, offers an effect method to greatly reduce SPAM at the point of entry (your server). IMO this is a better approach than using filter management within an e-mail client to deal with SPAM.
As for BT being a rude technology, I can only say that is a personal opinion. It has not been an issue for my business clients or friends as they are automatically white listed by the software after the initial challenge. Unless your clients or friends are changing their e-mails on a weekly basis I don't see how this can be an aggravating or complex issue for reasonable and intelligent people.