Fix mailoutbox fixture initialization with database-dependent fixtures

pytest_django/plugin.py

@@ -646,12 +646,18 @@ def _dj_autoclear_mailbox() -> None:
 
 @pytest.fixture
 def mailoutbox(
+    request: pytest.FixtureRequest,
     django_mail_patch_dns: None,  # noqa: ARG001
     _dj_autoclear_mailbox: None,
 ) -> list[django.core.mail.EmailMessage] | None:
     """A clean email outbox to which Django-generated emails are sent."""
     skip_if_no_django()
 
+    # Django's TestCase._pre_setup() replaces mail.outbox. Run the database
+    # helper first so mailoutbox returns the replacement list.
+    if "_django_db_helper" in request.fixturenames:
+        request.getfixturevalue("_django_db_helper")
+
     from django.core import mail
 
     if hasattr(mail, "outbox"):

tests/test_fixtures.py

@@ -804,6 +804,23 @@ def test_mail_again(mailoutbox) -> None:
     test_mail(mailoutbox)
 
 
+def test_mailoutbox_with_db(mailoutbox, db: None) -> None:  # noqa: ARG001
+    assert mailoutbox is mail.outbox
+
+
+@pytest.fixture
+def mail_sending_db_fixture(db: None) -> None:  # noqa: ARG001
+    mail.send_mail("subject", "body", "from@example.com", ["to@example.com"])
+
+
+def test_mailoutbox_with_db_dependent_fixture(
+    mailoutbox,
+    mail_sending_db_fixture: None,  # noqa: ARG001
+) -> None:
+    assert mailoutbox is mail.outbox
+    assert len(mailoutbox) == 1
+
+
 def test_mail_message_uses_mocked_DNS_NAME(mailoutbox) -> None:
     mail.send_mail("subject", "body", "from@example.com", ["to@example.com"])
     m = mailoutbox[0]