Crossposterous

Crossposterous will cross-post your WordPress blog post to your Posterous site. You can choose whether to post a teaser with a link back your WordPress blog post or cross-post the full content.

Configuration

1. Enter your Posterous email and password (used to log into http://posterous.com)
2. Select the site from the drop-down
3. Chose "Link back to post" or "Post full content"