The Simple Facebook Connect plugin is the best way I've come across to automatically update your Facebook wall and/or fan page when you post. It seems to do a better job than the Facebook plugin, and is free unlike Network Publisher who recently reduced the number of networks you can share on for free dramatically.
However, Simple Facebook Connect uses an evil hack to generate OpenGraph tags based on a WordPress post's contents that causes the post to be generated twice internally. This causes subtle conflicts with many other plugins, including MailPress. Plenty of other plugins can generate OpenGraph tags, but you can't have more than one doing the job at any time and there's currently no automatic way to arbitrate between them, so we need a way to disable this feature in every plugin that supports it.
However, you can work around this by adding the following code to your WordPress theme's functions.php:
/* Turn off Simple Facebook Connects evil OpenGraph tag generation */
Then enable OpenGraph tag generation in one of the other plugins capable of doing it. My current recommendation is to enable it in WordPress SEO by Yoast.