When an Privacy Lists does match Openfire seems just to drop messages. For the sending user it's a "black hole". In my opinion a "SHOULD" in XMPP should also implemented.

XEP-0016 (Privacy Lists) says:
( http://www.xmpp.org/extensions/xep-0016.html#protocol-error )

For message stanzas, the server SHOULD return an error, which SHOULD be <service-unavailable/>. [6]

reference [6] says:

6. Until version 1.5 of this document (therefore also in RFC 3921), it was recommended to silently ignore message stanzas, which unfortunately resulted in a delivery "black hole" regarding message stanzas.