I put zero time into it. I created a brand new Posterous account, left everything as the default and posted the email address tied to the account here.
I believe the default requires authorizing your posts. That may be the issue.
hm. well, if i had to venture a guess, i would say that it was because you used gmail exclusively, while mr curtis does not. probably easier to slide by if you're a poster who emails through various different clients over time.