WordPress MU (the multi-user/multi-blog version of WordPress) supports a basic post by email feature but it involves each user setting up their account to go out to an external email address and picking up the email. This seems rather “backwards” as it means your WPMU server is having to go out to find your new posts, and if you’ve got a lot of blogs then that’s potentially a lot of outgoing POP3 requests and it means that your have got the email account and passwords for your users, which some might see as not being a very good idea. WPMU suggest using a specific account to support posting by email and keeping the account “secret”.