We know that email can be an important channel for you to use to communicate with your users. To improve this channel, we've enhanced application email, letting you provide your users who've opted in to receive email from your application with a richer messaging experience.
You can now incorporate a number of HTML tags so you can format your messages as you see fit. Also, we've expanded the set of FBML tags you can include in your email messages -- including the new fb:restricted-to tag so you can extend the Demographic Restrictions feature to your email communication. Check the Developer Wiki to see the complete list of which tags you can and can't use.
In addition, you can use some FBML tags in your email subject lines like fb:name, so you can make your messages more personal. You can also use internationalization tags if you want to have your application translated into other languages.
Finally, now that users have to explicitly grant your application permission to send them email, we've eliminated the limit on how many messages you can send to a user in a given day. The number of messages you can send to users who added your application on the old profile are still limited; use admin.getAllocation to see how many messages you can send to those users.
Remember that email must still adhere to all applicable policies, including the Developer Terms of Service and Platform Policy.
Start testing these features today. As always, please send us any feedback on the Developer Forum.