✨(mailbox) remove secondary email as required field

The secondary email address is no longer required for all creation
processes and we should not force the user to provide and store an
insecure email address.

src/backend/mailbox_manager/tests/api/mailboxes/test_api_mailboxes_create.py

@@ -197,7 +197,7 @@ def test_api_mailboxes__create_with_accent_success(role):
 def test_api_mailboxes__create_administrator_missing_fields():
     """
     Administrator users should not be able to create mailboxes
-    without local part or secondary mail.
+    without local part.
     """
     mail_domain = factories.MailDomainEnabledFactory()
     access = factories.MailDomainAccessFactory(
@@ -219,18 +219,54 @@ def test_api_mailboxes__create_administrator_missing_fields():
     assert not models.Mailbox.objects.exists()
     assert response.json() == {"local_part": ["This field is required."]}
 
+
+@responses.activate
+@pytest.mark.parametrize(
+    "role",
+    [enums.MailDomainRoleChoices.OWNER, enums.MailDomainRoleChoices.ADMIN],
+)
+def test_api_mailboxes__create_without_secondary_email(role, caplog):
+    """
+    Creating a new mailbox should not require a secondary email.
+    We should be able to create a mailbox but not send any email notification.
+    """
+    mail_domain = factories.MailDomainEnabledFactory()
+    access = factories.MailDomainAccessFactory(role=role, domain=mail_domain)
+    client = APIClient()
+    client.force_login(access.user)
     mailbox_values = serializers.MailboxSerializer(
         factories.MailboxFactory.build()
     ).data
     del mailbox_values["secondary_email"]
+
+    responses.add(
+        responses.GET,
+        re.compile(r".*/token/"),
+        body=TOKEN_OK,
+        status=status.HTTP_200_OK,
+        content_type="application/json",
+    )
+    responses.add(
+        responses.POST,
+        re.compile(rf".*/domains/{mail_domain.name}/mailboxes/"),
+        body=response_mailbox_created(
+            f"{mailbox_values['local_part']}@{mail_domain.name}"
+        ),
+        status=status.HTTP_201_CREATED,
+        content_type="application/json",
+    )
     response = client.post(
         f"/api/v1.0/mail-domains/{mail_domain.slug}/mailboxes/",
         mailbox_values,
         format="json",
     )
-    assert response.status_code == status.HTTP_400_BAD_REQUEST
-    assert not models.Mailbox.objects.exists()
-    assert response.json() == {"secondary_email": ["This field is required."]}
+    assert response.status_code == status.HTTP_201_CREATED
+    mailbox = models.Mailbox.objects.get()
+    assert (
+        caplog.records[0].message
+        == f"Email notification for {mailbox} creation not sent "
+        "because no secondary email found"
+    )
 
 
 @pytest.mark.parametrize(

src/backend/mailbox_manager/tests/models/test_mailboxes.py

@@ -81,18 +81,6 @@ def test_models_mailboxes__domain_cannot_be_null():
 # SECONDARY_EMAIL FIELD
 
 
-def test_models_mailboxes__secondary_email_cannot_be_empty():
-    """The "secondary_email" field should not be empty."""
-    with pytest.raises(exceptions.ValidationError, match="This field cannot be blank"):
-        factories.MailboxFactory(secondary_email="")
-
-
-def test_models_mailboxes__secondary_email_cannot_be_null():
-    """The "secondary_email" field should not be null."""
-    with pytest.raises(exceptions.ValidationError, match="This field cannot be null"):
-        factories.MailboxFactory(secondary_email=None)
-
-
 @pytest.mark.parametrize(
     "domain_status",
     [