diff --git a/Makefile b/Makefile
index 2ae1be6..55c5aba 100644
--- a/Makefile
+++ b/Makefile
@@ -63,16 +63,22 @@ SOPEL_SELECTORS := \
 # testNoticeNonexistentChannel fails: https://bugs.unrealircd.org/view.php?id=5949
 # test_regressions::testTagCap fails: https://bugs.unrealircd.org/view.php?id=5948
 # test_messages::testLineTooLong fails: https://bugs.unrealircd.org/view.php?id=5947
-UNREAL_SELECTORS := \
+# testCapRemovalByClient and testNakWhole fail pending https://github.com/unrealircd/unrealircd/pull/148
+# Tests marked with arbitrary_client_tags can't pass because Unreal whitelists tags it relays
+UNREALIRCD_SELECTORS := \
 	not Ergo \
+	and not deprecated \
+	and not strict \
 	and not testNoticeNonexistentChannel \
 	and not (test_regressions and testTagCap) \
 	and not (test_messages and testLineTooLong) \
+	and not (test_cap and (testCapRemovalByClient or testNakWhole)) \
+	and not arbitrary_client_tags \
 	$(EXTRA_SELECTORS)
 
-.PHONY: all flakes ergo charybdis
+.PHONY: all flakes charybdis ergo inspircd mammon limnoria sopel solanum unrealircd
 
-all: flakes ergo inspircd limnoria sopel solanum
+all: flakes charybdis ergo inspircd mammon limnoria sopel solanum unrealircd
 
 flakes:
 	pyflakes3 irctest
@@ -97,3 +103,6 @@ solanum:
 
 sopel:
 	$(PYTEST) $(PYTEST_ARGS) --controller=irctest.controllers.sopel -k '$(SOPEL_SELECTORS)'
+
+unrealircd:
+	$(PYTEST) $(PYTEST_ARGS) --controller=irctest.controllers.unrealircd -k '$(UNREALIRCD_SELECTORS)'
diff --git a/irctest/basecontrollers.py b/irctest/basecontrollers.py
index adc5371..fa59bbd 100644
--- a/irctest/basecontrollers.py
+++ b/irctest/basecontrollers.py
@@ -183,6 +183,8 @@ class BaseServerController(_BaseController):
     port: int
     hostname: str
     services_controller: BaseServicesController
+    extban_mute_char: Optional[str] = None
+    """Character used for the 'mute' extban"""
 
     def run(
         self,
diff --git a/irctest/controllers/charybdis.py b/irctest/controllers/charybdis.py
index 3e84c5b..5094e94 100644
--- a/irctest/controllers/charybdis.py
+++ b/irctest/controllers/charybdis.py
@@ -73,6 +73,7 @@ class CharybdisController(BaseServerController, DirectoryBasedController):
     binary_name = "charybdis"
     supported_sasl_mechanisms = {"PLAIN"}
     supports_sts = False
+    extban_mute_char = None
 
     def create_config(self) -> None:
         super().create_config()
diff --git a/irctest/controllers/inspircd.py b/irctest/controllers/inspircd.py
index d28f13f..2186483 100644
--- a/irctest/controllers/inspircd.py
+++ b/irctest/controllers/inspircd.py
@@ -68,6 +68,7 @@ class InspircdController(BaseServerController, DirectoryBasedController):
     software_name = "InspIRCd"
     supported_sasl_mechanisms = {"PLAIN"}
     supports_sts = False
+    extban_mute_char = "m"
 
     def create_config(self) -> None:
         super().create_config()
diff --git a/irctest/controllers/unrealircd.py b/irctest/controllers/unrealircd.py
index 2f38e6c..da859cd 100644
--- a/irctest/controllers/unrealircd.py
+++ b/irctest/controllers/unrealircd.py
@@ -78,14 +78,17 @@ set {{
     default-server "irc.example.org";
     help-channel "#Help";
     cloak-keys {{ "aaaA1"; "bbbB2"; "cccC3"; }}
-        anti-flood {{
-            // Prevent throttling, especially test_buffering.py which
-            // triggers anti-flood with its very long lines
-            unknown-users {{
-                lag-penalty 1;
-                lag-penalty-bytes 10000;
-            }}
+    options {{
+        identd-check;  // Disable it, so it doesn't prefix idents with a tilde
+    }}
+    anti-flood {{
+        // Prevent throttling, especially test_buffering.py which
+        // triggers anti-flood with its very long lines
+        unknown-users {{
+            lag-penalty 1;
+            lag-penalty-bytes 10000;
         }}
+    }}
 }}
 
 tld {{
@@ -102,6 +105,8 @@ class UnrealircdController(BaseServerController, DirectoryBasedController):
     supported_sasl_mechanisms = {"PLAIN"}
     supports_sts = False
 
+    extban_mute_char = "q"
+
     def create_config(self) -> None:
         super().create_config()
         with self.open_file("server.conf"):
@@ -170,7 +175,7 @@ class UnrealircdController(BaseServerController, DirectoryBasedController):
         )
 
         if run_services:
-            assert False
+            raise NotImplementedByController("Registration services")
 
 
 def get_irctest_controller_class() -> Type[UnrealircdController]:
diff --git a/irctest/patma.py b/irctest/patma.py
index 37225ba..19a4780 100644
--- a/irctest/patma.py
+++ b/irctest/patma.py
@@ -54,6 +54,15 @@ ANYDICT = {RemainingKeys(ANYSTR): AnyOptStr()}
 `match_dict(got_tags, {"label": "foo", **ANYDICT})`"""
 
 
+class _AnyListRemainder:
+    def __repr__(self) -> str:
+        return "*ANYLIST"
+
+
+ANYLIST = [_AnyListRemainder()]
+"""Matches any list remainder"""
+
+
 def match_string(got: Optional[str], expected: Union[str, Operator, None]) -> bool:
     if isinstance(expected, AnyOptStr):
         return True
@@ -78,6 +87,9 @@ def match_list(
     The ANYSTR operator can be used on the 'expected' side as a wildcard,
     matching any *single* value; and StrRe("<regexp>") can be used to match regular
     expressions"""
+    if expected[-1] is ANYLIST[0]:
+        expected = expected[0:-1]
+        got = got[0 : len(expected)]  # Ignore remaining
     if len(got) != len(expected):
         return False
     return all(
diff --git a/irctest/server_tests/test_channel_operations.py b/irctest/server_tests/test_channel_operations.py
index 8415441..c683d5f 100644
--- a/irctest/server_tests/test_channel_operations.py
+++ b/irctest/server_tests/test_channel_operations.py
@@ -26,7 +26,7 @@ from irctest.numerics import (
     RPL_TOPIC,
     RPL_TOPICTIME,
 )
-from irctest.patma import ANYSTR, StrRe
+from irctest.patma import ANYLIST, ANYSTR, StrRe
 
 MODERN_CAPS = [
     "server-time",
@@ -1296,16 +1296,13 @@ class OpModerated(cases.BaseServerTestCase):
 class MuteExtban(cases.BaseServerTestCase):
     """https://defs.ircdocs.horse/defs/isupport.html#extban
 
-    These tests assume that if the server advertizes the 'm' extban,
-    then it supports mute.
+    It magically guesses what char the IRCd uses for mutes."""
 
-    This is not true of Charybdis, which introduced a conflicting 'm'
-    exban for matching hostmasks in 2015
-    (e2a9fa9cab3720215d8081e940109416e8214a29).
-
-    But Unreal was already using 'm' for muting since 2008
-    (f474e7e6dc2d36f96150ebe33b23b4ea76814415) and it is the most popular
-    definition so we're going with that one."""
+    def char(self):
+        if self.controller.extban_mute_char is None:
+            raise runner.ExtbanNotSupported("", "mute")
+        else:
+            return self.controller.extban_mute_char
 
     @cases.mark_specifications("Ergo")
     def testISupport(self):
@@ -1313,7 +1310,7 @@ class MuteExtban(cases.BaseServerTestCase):
         isupport = self.server_support
         token = isupport["EXTBAN"]
         prefix, comma, types = token.partition(",")
-        self.assertIn("m", types, "Missing 'm' in ISUPPORT EXTBAN")
+        self.assertIn(self.char, types, f"Missing '{self.char()}' in ISUPPORT EXTBAN")
         self.assertEqual(prefix, "")
         self.assertEqual(comma, ",")
 
@@ -1325,15 +1322,15 @@ class MuteExtban(cases.BaseServerTestCase):
         isupport = self.server_support
         token = isupport.get("EXTBAN", "")
         prefix, comma, types = token.partition(",")
-        if "m" not in types:
-            raise runner.ExtbanNotSupported("m", "mute")
+        if self.char() not in types:
+            raise runner.ExtbanNotSupported(self.char(), "mute")
 
         clients = ("chanop", "bar")
 
         # Mute "bar"
         self.joinChannel("chanop", "#chan")
         self.getMessages("chanop")
-        self.sendLine("chanop", "MODE #chan +b m:bar!*@*")
+        self.sendLine("chanop", f"MODE #chan +b {prefix}{self.char()}:bar!*@*")
         replies = {msg.command for msg in self.getMessages("chanop")}
         self.assertIn("MODE", replies)
         self.assertNotIn(ERR_CHANOPRIVSNEEDED, replies)
@@ -1344,6 +1341,21 @@ class MuteExtban(cases.BaseServerTestCase):
         for client in clients:
             self.getMessages(client)
 
+        # "bar" sees the MODE too
+        self.sendLine("bar", "MODE #chan +b")
+        self.assertMessageMatch(
+            self.getMessage("bar"),
+            command="367",
+            params=[
+                "bar",
+                "#chan",
+                f"{prefix}{self.char()}:bar!*@*",
+                "chanop",
+                *ANYLIST,
+            ],
+        )
+        self.getMessages("bar")
+
         # "bar" talks: rejected
         self.sendLine("bar", "PRIVMSG #chan :hi from bar")
         replies = self.getMessages("bar")
@@ -1354,7 +1366,7 @@ class MuteExtban(cases.BaseServerTestCase):
 
         # remove mute on "bar" with -b
         self.getMessages("chanop")
-        self.sendLine("chanop", "MODE #chan -b m:bar!*@*")
+        self.sendLine("chanop", f"MODE #chan -b {prefix}{self.char()}:bar!*@*")
         replies = {msg.command for msg in self.getMessages("chanop")}
         self.assertIn("MODE", replies)
         self.assertNotIn(ERR_CHANOPRIVSNEEDED, replies)
@@ -1378,15 +1390,15 @@ class MuteExtban(cases.BaseServerTestCase):
         isupport = self.server_support
         token = isupport.get("EXTBAN", "")
         prefix, comma, types = token.partition(",")
-        if "m" not in types:
-            raise runner.ExtbanNotSupported("m", "mute")
+        if self.char() not in types:
+            raise runner.ExtbanNotSupported(self.char(), "mute")
 
         clients = ("chanop", "qux")
 
         # Mute "qux"
         self.joinChannel("chanop", "#chan")
         self.getMessages("chanop")
-        self.sendLine("chanop", "MODE #chan +b m:qux!*@*")
+        self.sendLine("chanop", f"MODE #chan +b {prefix}{self.char()}:qux!*@*")
         replies = {msg.command for msg in self.getMessages("chanop")}
         self.assertIn("MODE", replies)
         self.assertNotIn(ERR_CHANOPRIVSNEEDED, replies)
@@ -1437,17 +1449,17 @@ class MuteExtban(cases.BaseServerTestCase):
         isupport = self.server_support
         token = isupport.get("EXTBAN", "")
         prefix, comma, types = token.partition(",")
-        if "m" not in types:
-            raise runner.ExtbanNotSupported("m", "mute")
+        if self.char() not in types:
+            raise runner.ExtbanNotSupported(self.char(), "mute")
         if "e" not in self.server_support["CHANMODES"]:
-            raise runner.ChannelModeNotSupported("m", "mute")
+            raise runner.ChannelModeNotSupported(self.char(), "mute")
 
         clients = ("chanop", "qux")
 
         # Mute "qux"
         self.joinChannel("chanop", "#chan")
         self.getMessages("chanop")
-        self.sendLine("chanop", "MODE #chan +b m:qux!*@*")
+        self.sendLine("chanop", f"MODE #chan +b {prefix}{self.char()}:qux!*@*")
         replies = {msg.command for msg in self.getMessages("chanop")}
         self.assertIn("MODE", replies)
         self.assertNotIn(ERR_CHANOPRIVSNEEDED, replies)
@@ -1472,11 +1484,13 @@ class MuteExtban(cases.BaseServerTestCase):
             self.getMessages(client)
 
         # +e grants an exemption to +b
-        self.sendLine("chanop", "MODE #chan +e m:*!~evan@*")
+        self.sendLine("chanop", f"MODE #chan +e {prefix}{self.char()}:*!~evan@*")
         replies = {msg.command for msg in self.getMessages("chanop")}
         self.assertIn("MODE", replies)
         self.assertNotIn(ERR_CHANOPRIVSNEEDED, replies)
 
+        self.getMessages("qux")
+
         # so "qux" can now talk
         self.sendLine("qux", "PRIVMSG #chan :thanks for mute-excepting me")
         replies = self.getMessages("qux")
@@ -1499,10 +1513,14 @@ class MuteExtban(cases.BaseServerTestCase):
         """
         clients = ("chanop", "bar")
 
+        isupport = self.server_support
+        token = isupport.get("EXTBAN", "")
+        prefix, comma, types = token.partition(",")
+
         self.connectClient("chanop", name="chanop")
         self.joinChannel("chanop", "#chan")
         self.getMessages("chanop")
-        self.sendLine("chanop", "MODE #chan +b m:BAR!*@*")
+        self.sendLine("chanop", f"MODE #chan +b {prefix}{self.char()}:BAR!*@*")
         replies = {msg.command for msg in self.getMessages("chanop")}
         self.assertIn("MODE", replies)
         self.assertNotIn(ERR_CHANOPRIVSNEEDED, replies)
@@ -1521,7 +1539,7 @@ class MuteExtban(cases.BaseServerTestCase):
         self.assertEqual(self.getMessages("chanop"), [])
 
         # remove mute with -b
-        self.sendLine("chanop", "MODE #chan -b m:bar!*@*")
+        self.sendLine("chanop", f"MODE #chan -b {prefix}{self.char()}:bar!*@*")
         replies = {msg.command for msg in self.getMessages("chanop")}
         self.assertIn("MODE", replies)
         self.assertNotIn(ERR_CHANOPRIVSNEEDED, replies)
diff --git a/irctest/server_tests/test_connection_registration.py b/irctest/server_tests/test_connection_registration.py
index ce2acde..40b8b59 100644
--- a/irctest/server_tests/test_connection_registration.py
+++ b/irctest/server_tests/test_connection_registration.py
@@ -119,15 +119,38 @@ class ConnectionRegistrationTestCase(cases.BaseServerTestCase):
         self.sendLine(2, "NICK foo")
         self.sendLine(1, "USER username * * :Realname")
         self.sendLine(2, "USER username * * :Realname")
-        m1 = self.getRegistrationMessage(1)
-        m2 = self.getRegistrationMessage(2)
+
+        try:
+            m1 = self.getRegistrationMessage(1)
+        except (ConnectionClosed, ConnectionResetError):
+            # Unreal closes the connection, see
+            # https://bugs.unrealircd.org/view.php?id=5950
+            command1 = None
+        else:
+            command1 = m1.command
+
+        try:
+            m2 = self.getRegistrationMessage(2)
+        except (ConnectionClosed, ConnectionResetError):
+            # ditto
+            command2 = None
+        else:
+            command2 = m2.command
+
         self.assertNotEqual(
-            (m1.command, m2.command),
+            (command1, command2),
             ("001", "001"),
             "Two concurrently registering requesting the same nickname "
             "both got 001.",
         )
 
+        self.assertIn(
+            "001",
+            (command1, command2),
+            "Two concurrently registering requesting the same nickname "
+            "neither got 001.",
+        )
+
     @cases.mark_specifications("IRCv3")
     def testIrc301CapLs(self):
         """
diff --git a/irctest/server_tests/test_echo_message.py b/irctest/server_tests/test_echo_message.py
index d43aafa..4226697 100644
--- a/irctest/server_tests/test_echo_message.py
+++ b/irctest/server_tests/test_echo_message.py
@@ -2,6 +2,8 @@
 <http://ircv3.net/specs/extensions/echo-message-3.2.html>
 """
 
+import pytest
+
 from irctest import cases
 from irctest.basecontrollers import NotImplementedByController
 from irctest.irc_utils.junkdrawer import random_name
@@ -97,6 +99,7 @@ def _testEchoMessage(command, solo, server_time):
 
 
 class EchoMessageTestCase(cases.BaseServerTestCase):
+    @pytest.mark.arbitrary_client_tags
     @cases.mark_capabilities(
         "batch", "labeled-response", "echo-message", "message-tags"
     )
diff --git a/irctest/server_tests/test_labeled_responses.py b/irctest/server_tests/test_labeled_responses.py
index ad4274c..239abf5 100644
--- a/irctest/server_tests/test_labeled_responses.py
+++ b/irctest/server_tests/test_labeled_responses.py
@@ -282,7 +282,14 @@ class LabeledResponsesTestCase(cases.BaseServerTestCase, cases.OptionalityHelper
         )
         self.getMessages(2)
 
-        self.sendLine(1, "@label=12345;+draft/reply=123;+draft/react=l😃l TAGMSG bar")
+        # Need to get a valid msgid because Unreal validates them
+        self.sendLine(1, "PRIVMSG bar :hi")
+        msgid = self.getMessage(1).tags["msgid"]
+        assert msgid == self.getMessage(2).tags["msgid"]
+
+        self.sendLine(
+            1, f"@label=12345;+draft/reply={msgid};+draft/react=l😃l TAGMSG bar"
+        )
         m = self.getMessage(1)
         m2 = self.getMessage(2)
 
@@ -290,7 +297,7 @@ class LabeledResponsesTestCase(cases.BaseServerTestCase, cases.OptionalityHelper
         self.assertMessageMatch(
             m2,
             command="TAGMSG",
-            tags={"+draft/reply": "123", "+draft/react": "l😃l", **ANYDICT},
+            tags={"+draft/reply": msgid, "+draft/react": "l😃l", **ANYDICT},
         )
         self.assertNotIn(
             "label",
@@ -308,7 +315,7 @@ class LabeledResponsesTestCase(cases.BaseServerTestCase, cases.OptionalityHelper
             command="TAGMSG",
             tags={
                 "label": "12345",
-                "+draft/reply": "123",
+                "+draft/reply": msgid,
                 "+draft/react": "l😃l",
                 **ANYDICT,
             },
@@ -338,7 +345,14 @@ class LabeledResponsesTestCase(cases.BaseServerTestCase, cases.OptionalityHelper
         self.getMessages(2)
         self.getMessages(1)
 
-        self.sendLine(1, "@label=12345;+draft/reply=123;+draft/react=l😃l TAGMSG #test")
+        # Need to get a valid msgid because Unreal validates them
+        self.sendLine(1, "PRIVMSG #test :hi")
+        msgid = self.getMessage(1).tags["msgid"]
+        assert msgid == self.getMessage(2).tags["msgid"]
+
+        self.sendLine(
+            1, f"@label=12345;+draft/reply={msgid};+draft/react=l😃l TAGMSG #test"
+        )
         ms = self.getMessage(1)
         mt = self.getMessage(2)
 
@@ -361,7 +375,9 @@ class LabeledResponsesTestCase(cases.BaseServerTestCase, cases.OptionalityHelper
 
         # ensure sender correctly receives msg
         self.assertMessageMatch(
-            ms, command="TAGMSG", tags={"label": "12345", **ANYDICT}
+            ms,
+            command="TAGMSG",
+            tags={"label": "12345", "+draft/reply": msgid, **ANYDICT},
         )
 
     @cases.mark_capabilities(
diff --git a/irctest/server_tests/test_message_tags.py b/irctest/server_tests/test_message_tags.py
index ce190f7..a0f4745 100644
--- a/irctest/server_tests/test_message_tags.py
+++ b/irctest/server_tests/test_message_tags.py
@@ -2,6 +2,8 @@
 https://ircv3.net/specs/extensions/message-tags.html
 """
 
+import pytest
+
 from irctest import cases
 from irctest.irc_utils.message_parser import parse_message
 from irctest.numerics import ERR_INPUTTOOLONG
@@ -9,6 +11,7 @@ from irctest.patma import ANYDICT, ANYSTR, StrRe
 
 
 class MessageTagsTestCase(cases.BaseServerTestCase, cases.OptionalityHelper):
+    @pytest.mark.arbitrary_client_tags
     @cases.mark_capabilities("message-tags")
     def testBasic(self):
         def getAllMessages():
@@ -107,6 +110,7 @@ class MessageTagsTestCase(cases.BaseServerTestCase, cases.OptionalityHelper):
             self.assertNotIn("cat", msg.tags)
         self.assertEqual(alice_msg.tags["msgid"], bob_msg.tags["msgid"])
 
+    @pytest.mark.arbitrary_client_tags
     @cases.mark_capabilities("message-tags")
     @cases.mark_specifications("ircdocs")
     def testLengthLimits(self):
diff --git a/pytest.ini b/pytest.ini
index 9eb742d..eadf6f4 100644
--- a/pytest.ini
+++ b/pytest.ini
@@ -12,6 +12,7 @@ markers =
     strict
     deprecated
     services
+    arbitrary_client_tags
 
     # capabilities
     account-tag