--- a/plugins/mod_s2s.lua	Wed Mar 11 16:59:10 2026 +0100
+++ b/plugins/mod_s2s.lua	Sun Mar 22 11:28:52 2026 +0100
@@ -19,7 +19,7 @@
 local stop_timer = require "prosody.util.timer".stop;
 local st = require "prosody.util.stanza";
 local initialize_filters = require "prosody.util.filters".initialize;
-local nameprep = require "prosody.util.encodings".stringprep.nameprep;
+local prepped_split = require "prosody.util.jid".prepped_split;
 local new_xmpp_stream = require "prosody.util.xmppstream".new;
 local s2s_new_incoming = require "prosody.core.s2smanager".new_incoming;
 local s2s_new_outgoing = require "prosody.core.s2smanager".new_outgoing;
@@ -511,8 +511,12 @@
 
 		-- Validate to/from
 		local to, from = attr.to, attr.from;
-		if to then to = nameprep(attr.to); end
-		if from then from = nameprep(attr.from); end
+		local function hostprep(s)
+			local node, host, res = prepped_split(s);
+			if not (node or res) then return host; end
+		end
+		if to then to = hostprep(attr.to); end
+		if from then from = hostprep(attr.from); end
 		if not to and attr.to then -- COMPAT: Some servers do not reliably set 'to' (especially on stream restarts)
 			session:close({ condition = "improper-addressing", text = "Invalid 'to' address" });
 			return;

--- a/spec/util_jid_spec.lua	Wed Mar 11 16:59:10 2026 +0100
+++ b/spec/util_jid_spec.lua	Sun Mar 22 11:28:52 2026 +0100
@@ -79,6 +79,7 @@
 			test("xmpp:test@example.com", nil, nil, nil);
 			test("xmpp:example.com", nil, nil, nil);
 			test("+123@bridge.example.com)", nil, nil, nil);
+			test("node@2001:db8::50:726f:736f:6479/foo", nil, nil, nil);
 		end);
 		it("should reject invalid arguments", function ()
 			assert.has_error(function () jid.prepped_split(false) end)

--- a/util/jid.lua	Wed Mar 11 16:59:10 2026 +0100
+++ b/util/jid.lua	Sun Mar 22 11:28:52 2026 +0100
@@ -52,7 +52,8 @@
 
 local function valid_ip(ip)
 	local v6 = match(ip, "^%[([%x:.]+)%]$");
-	return net.pton(v6 or ip);
+	local v4 = match(ip, "^%d%d?%d?%.%d%d?%d?%.%d%d?%d?%.%d%d?%d?$");
+	return (v6 or v4) and net.pton(v6 or v4);
 end
 
 local function prepped_split(jid, strict)