Once the email address are added to the team site then just send an email to post@orioles.posterous.com and everyone will get it.  It can also be setup to send a text message through twitter.com.  When you do this it is also posted to the web site.  Just reply and the message is again sent to the whole team and the web site is updated.  Want a private message not on the web site then sent to private@orioles.posterous.com.

See http://blog.posterous.com/posterous-group-blogs-are-now-email-lists-too for more info.