IANAL, but the notion of "strict liability" horrified me when I first head of it, and I thought it had to be some kind of a misunderstanding. So we're tossing that "innocent until proven guilty" idea out the window, huh?
I'm sure smarter people than me have sussed this out and can explain why it's a good thing, but it sits wrong with me. We can put the subject matter aside for a second: I don't think I could convict someone for having something happen to them, regardless of what the law says. Let's say drug possession was a strict liability law (and maybe it is for all I know). Finding a baggy of meth on the corner of a farmer's lot would mean that, technically, he was guilty of possession and had to prove that it wasn't really is. That's nuts. And looping back to the subject at hand, if the only evidence that someone possessed CSAM was their email inbox, without proof that it was solicited? They want me on their jury.
There should never be a circumstance where someone can't report something that happened to them to the police without a legitimate fear of being arrested. That's bad for the person, and it's bad for society.
But if their hard drive has folders grouped by age or something, prepare the solar catapult.