How does Posterous know that what I'm emailing hasn't been spoofed?

When I email Posterous with content to post, how do they know it's really me?

Their FAQ reads:

"E开发者_StackOverflow社区mail can easily be spoofed, but Posterous has come up with some ways to figure out if the email we receive comes from you. If we think it might not be you, we ask you to confirm the email before we post it."

Probably the same way spam detection works nowadays, but using a probabilistic classifier, such as a Bayes classifier, applied to both the actual content and things like the address it was sent on, client identification, geolocation etc.

Whatever it is, only they can tell you - why not ask them?