I can't blame people for using spam-fighting tools, but there's one particularly annoying that is, sadly, not yet dead: those "challenge" systems that require an email recipient to approve you as a sender. I sent an email to about ten people this morning (a "reply all" to a group of people on a committee of a non-profit organization whose board I'm on) and promptly got this irritating Earthlink-generated "I'm sorry, but you must be approved to send me email, please feel out this form!" (complete with a captcha field).
My first thought was, "You're just not important enough to have to fill out a form because you're cc'ed on an email, buddy."
I find these things seriously annoying. They popped up a few years ago but I rarely see them anymore. Part of the reasons for that, I suspect, is that they make you lose email you really want (order confirmation, newsletters, etc.) which you might have asked for, but are sent by automated systems that are not going to fill out your form.
It's a bit like having the mailman turn up at your door holding a birthday card you sent telling you, "I'm sorry, but we won't deliver this unless you show us an ID."
Let's hope they vanish completely soon.