Having several blogs can be a bit hard to maintain, and micro blogging services like Posterous and Tumblr provide a quicker way to post content to the web. However, WordPress has added features which are similar to Posterous in the form of post by email to WordPress.com blogs.

More at: http://weblogtoolscollection.com/archives/2010/02/08/wordpress-com-introduces-import-from-posterous/