provide helpful error message when option is disabled

src/sentry/users/web/accounts.py

@@ -6,7 +6,7 @@
 from django.contrib.auth import login as login_user
 from django.core.signing import BadSignature, SignatureExpired
 from django.db import router, transaction
-from django.http import HttpRequest, HttpResponse, HttpResponseNotFound, HttpResponseRedirect
+from django.http import HttpRequest, HttpResponse, HttpResponseRedirect
 from django.urls import reverse
 from django.utils.translation import gettext as _
 from django.views.decorators.http import require_http_methods
@@ -402,7 +402,10 @@ def confirm_signed_email(
 
     use_signed_urls = options.get("user-settings.signed-url-confirmation-emails")
     if not use_signed_urls:
-        return HttpResponseNotFound()
+        msg = ERR_CONFIRMING_EMAIL
+        level = messages.ERROR
+        messages.add_message(request, level, msg)
+        return HttpResponseRedirect(reverse("sentry-account-settings-emails"))
 
     msg = _("Thanks for confirming your email")
     level = messages.SUCCESS

tests/sentry/users/api/endpoints/test_user_emails_confirm.py

@@ -211,4 +211,11 @@ def test_confirm_email_signed_urls_disabled(self):
         resp = self.client.get(
             reverse("sentry-account-confirm-signed-email", args=[signed_data]), follow=True
         )
-        assert resp.status_code == 404
+        assert resp.status_code == 200
+
+        messages = list(resp.context["messages"])
+        assert len(messages) == 1
+        assert (
+            messages[0].message
+            == "There was an error confirming your email. Please try again or visit your Account Settings to resend the verification email."
+        )