diff --git a/openedx/core/djangoapps/user_authn/views/login.py b/openedx/core/djangoapps/user_authn/views/login.py
index d95fd2232e..7dc2136578 100644
--- a/openedx/core/djangoapps/user_authn/views/login.py
+++ b/openedx/core/djangoapps/user_authn/views/login.py
@@ -326,7 +326,15 @@ def _check_user_auth_flow(site, user):
     """
     if user and ENABLE_LOGIN_USING_THIRDPARTY_AUTH_ONLY.is_enabled():
         allowed_domain = site.configuration.get_value('THIRD_PARTY_AUTH_ONLY_DOMAIN', '').lower()
-        user_domain = user.email.split('@')[1].strip().lower()
+        email_parts = user.email.split('@')
+        if len(email_parts) != 2:
+            # User has a nonstandard email so we record their id.
+            # we don't record their e-mail in case there is sensitive info accidentally
+            # in there.
+            set_custom_metric('login_tpa_domain_shortcircuit_user_id', user.id)
+            log.warn("User %s has nonstandard e-mail. Shortcircuiting THIRD_PART_AUTH_ONLY_DOMAIN check.", user.id)
+            return
+        user_domain = email_parts[1].strip().lower()
 
         # If user belongs to allowed domain and not whitelisted then user must login through allowed domain SSO
         if user_domain == allowed_domain and not AllowedAuthUser.objects.filter(site=site, email=user.email).exists():
diff --git a/openedx/core/djangoapps/user_authn/views/tests/test_login.py b/openedx/core/djangoapps/user_authn/views/tests/test_login.py
index 3feff222dc..09d1c24894 100644
--- a/openedx/core/djangoapps/user_authn/views/tests/test_login.py
+++ b/openedx/core/djangoapps/user_authn/views/tests/test_login.py
@@ -30,7 +30,8 @@ from openedx.core.djangoapps.user_api.accounts import EMAIL_MIN_LENGTH, EMAIL_MA
 from openedx.core.djangoapps.user_authn.cookies import jwt_cookies
 from openedx.core.djangoapps.user_authn.views.login import (
     AllowedAuthUser,
-    ENABLE_LOGIN_USING_THIRDPARTY_AUTH_ONLY
+    ENABLE_LOGIN_USING_THIRDPARTY_AUTH_ONLY,
+    _check_user_auth_flow
 )
 from openedx.core.djangoapps.user_authn.tests.utils import setup_login_oauth_client
 from openedx.core.djangolib.testing.utils import CacheIsolationTestCase, skip_unless_lms
@@ -785,6 +786,28 @@ class LoginTest(SiteMixin, CacheIsolationTestCase):
                         )
                         self.assertFalse(mock_check_user_auth_flow.called)
 
+    def test_check_user_auth_flow_bad_email(self):
+        """Regression Exception was thrown on missing @ char in TPA."""
+        provider = 'Google'
+        provider_tpa_hint = 'saml-test'
+        username = 'batman'
+        invalid_email_user = self._create_user(username, username)
+        allowed_domain = 'edx.org'
+        default_site_configuration_values = {
+            'SITE_NAME': allowed_domain,
+            'THIRD_PARTY_AUTH_ONLY_DOMAIN': allowed_domain,
+            'THIRD_PARTY_AUTH_ONLY_PROVIDER': provider,
+            'THIRD_PARTY_AUTH_ONLY_HINT': provider_tpa_hint,
+        }
+
+        with ENABLE_LOGIN_USING_THIRDPARTY_AUTH_ONLY.override(True):
+            site = self.set_up_site(allowed_domain, default_site_configuration_values)
+
+            with self.assertLogs(level='WARN') as log:
+                _check_user_auth_flow(site, invalid_email_user)
+                assert len(log.output) == 1
+                assert "Shortcircuiting THIRD_PART_AUTH_ONLY_DOMAIN check." in log.output[0]
+
 
 @ddt.ddt
 @skip_unless_lms