BARIS is being a test case for a new sednmail milter: milter-sender.

The new filter performs a reverse check on the sending address’s primary mail server to verify that the sending address is legitimate and that the domain is willing to accept return mail. No actual return mail is sent, however if the tests fail then the incoming message is rejected. Other sanity checks are also performed. The primary result of this filter ought to be a decrease in the amount of spam coming from fake addresses, primarily at large domains such as Hotmail and Yahoo!. While most of this could be done in MIMEDefang, having a separate milter with this as its single function decreases complexity of the individual pieces. If testing procedes favorably on BARIS, we should be able to install this filter on KE as well.

Update: This milter does actually send a return message, contrary to the implications on the author’s web site (it is never stated that it doesn’t send this message, it is just somewhat implied). It also is not stable on BARIS, dying after a few days and unable to restart. For these reasons we won’t be using this milter.