Since Psi 0.12 does finally supports PrivacyLists without Bugs, I played a bit around with them.
For message stanzas, the server SHOULD return an error, which SHOULD be . 
reference  says:
- 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
Openfire seems just to drop messages. For the sending user it’s a “black hole”. In my optionion a “SHOULD” in XMPP should also implemented