diff --git a/anymail/checks.py b/anymail/checks.py
index 3c54e3b..da14efa 100644
--- a/anymail/checks.py
+++ b/anymail/checks.py
@@ -7,18 +7,20 @@ def check_deprecated_settings(app_configs, **kwargs):
 
     anymail_settings = getattr(settings, "ANYMAIL", {})
 
-    # anymail.W001: rename WEBHOOK_AUTHORIZATION to WEBHOOK_SECRET
+    # anymail.W001: reserved [was deprecation warning that became anymail.E001]
+
+    # anymail.E001: rename WEBHOOK_AUTHORIZATION to WEBHOOK_SECRET
     if "WEBHOOK_AUTHORIZATION" in anymail_settings:
-        errors.append(checks.Warning(
+        errors.append(checks.Error(
             "The ANYMAIL setting 'WEBHOOK_AUTHORIZATION' has been renamed 'WEBHOOK_SECRET' to improve security.",
-            hint="You must update your settings.py. The old name will stop working in a near-future release.",
-            id="anymail.W001",
+            hint="You must update your settings.py.",
+            id="anymail.E001",
         ))
     if hasattr(settings, "ANYMAIL_WEBHOOK_AUTHORIZATION"):
-        errors.append(checks.Warning(
+        errors.append(checks.Error(
             "The ANYMAIL_WEBHOOK_AUTHORIZATION setting has been renamed ANYMAIL_WEBHOOK_SECRET to improve security.",
-            hint="You must update your settings.py. The old name will stop working in a near-future release.",
-            id="anymail.W001",
+            hint="You must update your settings.py.",
+            id="anymail.E001",
         ))
 
     return errors
diff --git a/anymail/webhooks/base.py b/anymail/webhooks/base.py
index 30207e7..966c41c 100644
--- a/anymail/webhooks/base.py
+++ b/anymail/webhooks/base.py
@@ -26,9 +26,6 @@ class AnymailBasicAuthMixin(object):
     def __init__(self, **kwargs):
         self.basic_auth = get_anymail_setting('webhook_secret', default=[],
                                               kwargs=kwargs)  # no esp_name -- auth is shared between ESPs
-        if not self.basic_auth:
-            # Temporarily allow deprecated WEBHOOK_AUTHORIZATION setting
-            self.basic_auth = get_anymail_setting('webhook_authorization', default=[], kwargs=kwargs)
 
         # Allow a single string:
         if isinstance(self.basic_auth, six.string_types):
diff --git a/docs/installation.rst b/docs/installation.rst
index 803d3ff..5519e89 100644
--- a/docs/installation.rst
+++ b/docs/installation.rst
@@ -283,8 +283,9 @@ username or password for this shared secret.
 .. versionchanged:: 1.4
 
     The earlier WEBHOOK_AUTHORIZATION setting was renamed WEBHOOK_SECRET, so that
-    Django error reporting sanitizes it. The old name is still allowed in v1.4,
-    but will be removed in a near-future release. You should update your settings.
+    Django error reporting sanitizes it. Support for the old name was dropped in
+    Anymail 2.0, and if you have not yet updated your settings.py, all webhook calls
+    will fail with a "missing or invalid basic auth" error.
 
 
 .. setting:: ANYMAIL_REQUESTS_TIMEOUT
diff --git a/tests/test_checks.py b/tests/test_checks.py
index 8d31534..c6af934 100644
--- a/tests/test_checks.py
+++ b/tests/test_checks.py
@@ -11,17 +11,17 @@ class DeprecatedSettingsTests(SimpleTestCase, AnymailTestMixin):
     @override_settings(ANYMAIL={"WEBHOOK_AUTHORIZATION": "abcde:12345"})
     def test_webhook_authorization(self):
         errors = check_deprecated_settings(None)
-        self.assertEqual(errors, [checks.Warning(
+        self.assertEqual(errors, [checks.Error(
             "The ANYMAIL setting 'WEBHOOK_AUTHORIZATION' has been renamed 'WEBHOOK_SECRET' to improve security.",
-            hint="You must update your settings.py. The old name will stop working in a near-future release.",
-            id="anymail.W001",
+            hint="You must update your settings.py.",
+            id="anymail.E001",
         )])
 
     @override_settings(ANYMAIL_WEBHOOK_AUTHORIZATION="abcde:12345", ANYMAIL={})
     def test_anymail_webhook_authorization(self):
         errors = check_deprecated_settings(None)
-        self.assertEqual(errors, [checks.Warning(
+        self.assertEqual(errors, [checks.Error(
             "The ANYMAIL_WEBHOOK_AUTHORIZATION setting has been renamed ANYMAIL_WEBHOOK_SECRET to improve security.",
-            hint="You must update your settings.py. The old name will stop working in a near-future release.",
-            id="anymail.W001",
+            hint="You must update your settings.py.",
+            id="anymail.E001",
         )])
diff --git a/tests/webhook_cases.py b/tests/webhook_cases.py
index 0b8d0fb..e8f145c 100644
--- a/tests/webhook_cases.py
+++ b/tests/webhook_cases.py
@@ -125,9 +125,3 @@ class WebhookBasicAuthTestsMixin(object):
         self.set_basic_auth('baduser', 'wrongpassword')
         response = self.call_webhook()
         self.assertEqual(response.status_code, 400)
-
-    @override_settings(ANYMAIL={'WEBHOOK_AUTHORIZATION': "username:password"})
-    def test_deprecated_setting(self):
-        """The older WEBHOOK_AUTHORIZATION setting is still supported (for now)"""
-        response = self.call_webhook()
-        self.assertEqual(response.status_code, 200)