Dear Mr Palmer,
A) Either your blog's comment feature is broken, or navigation links to it have been misplaced. Please fix, so that I don't have to continue commenting here.
B) You are a spammer. You admit that you merrily sent spam on its way into around five user's inboxes - spam that you know appears to come from you, spam that you know is definitely unsolicited and unwanted. This makes you a spammer. The fact that you seem to think that sending this spam to users was somehow getting back at either the authors of the spam, or the writers of the spam blocking tools, only makes this worse.
C) You complain that "but the people whose job it is to write, maintain, and run spam software don't [know that source addresses are forged and there's no point replying to them]". If you'd take two seconds to think instead of sending spam and then blogging while enraged, you'd realise that this is patently false. The authors of these tools are trying to ensure that, in the case they've blocked legitimate email, it can be allowed through. This *requires* that they assume the From: address is not forged.
Please stop and think next time before you angry-blog.