#575 XEP-0191, mod_blocklist: MUST send error reply if user sends presence to blocked contact
Text just before example 9 says we MUST return an <not-acceptable/> error if a stanza is sent to a blocked contact. Currently presence stanzas are just dropped here. There may be a good reason for this which at least should be documented. Maybe due to server generated presence broadcasts passing by here which might spam the user with errors every time they move.
This text from XEP-0191:
If the user attempts to send an outbound stanza to the contact, the user's server MUST NOT route the stanza to the contact but instead MUST return a <not-acceptable/> error containing an application-specific error condition of <blocked/> qualified by the 'urn:xmpp:blocking:errors' namespace
I think fixing this requires changes to how mod_presence does broadcasting. Not sure how large tho.