[Rudism]

Agreed. You would have to pre-whitelist, or at least have a junk folder you could look in where non-captchad messages get stored for a certain amount of time before being purged so that you could fish out the emails from non-whitelisted addresses that you're actually expecting to get (and then presumably whitelist them from there for future emails).

[jiggy2011]

The problem with that is that you're actually going to look at email in your junk folder. Spammers would love this because they know that there's a chance that you'll actually see their crap even if it gets filtered.

The entire point of having a junk folder is you don't have to check it apart from the rare occasion you get a phone call saying "hey , I sent you an important email why haven't you replied?"