♻️(serializers) move dimail calls to serializers

we move all business logic from model to serializer.
all API calls (direct and from front) will keep on triggering
expected 3rd party calls while admin actions will uniquely trigger
modifications in our database.

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

@@ -4,6 +4,8 @@ Unit tests for the mailbox API
 
 import json
 import re
+from logging import Logger
+from unittest import mock
 
 from django.test.utils import override_settings
 
@@ -488,3 +490,59 @@ def test_api_mailboxes__handling_dimail_unexpected_error():
                 "detail": "Unexpected response from dimail: {'details': 'Internal server error'}"
             }
         assert not models.Mailbox.objects.exists()
+
+
+@mock.patch.object(Logger, "error")
+@mock.patch.object(Logger, "info")
+def test_api_mailboxes__send_correct_logger_infos(mock_info, mock_error):
+    """
+    Upon requesting mailbox creation, things are correctly logged
+    """
+    access = factories.MailDomainAccessFactory(role=enums.MailDomainRoleChoices.OWNER)
+
+    client = APIClient()
+    client.force_login(access.user)
+    mailbox_data = serializers.MailboxSerializer(
+        factories.MailboxFactory.build(domain=access.domain)
+    ).data
+
+    with responses.RequestsMock() as rsps:
+        # Ensure successful response using "responses":
+        rsps.add(
+            rsps.GET,
+            re.compile(r".*/token/"),
+            body='{"access_token": "domain_owner_token"}',
+            status=status.HTTP_200_OK,
+            content_type="application/json",
+        )
+        rsps.add(
+            rsps.POST,
+            re.compile(rf".*/domains/{access.domain.name}/mailboxes/"),
+            body=str(
+                {
+                    "email": f"{mailbox_data['local_part']}@{access.domain.name}",
+                    "password": "newpass",
+                    "uuid": "uuid",
+                }
+            ),
+            status=status.HTTP_201_CREATED,
+            content_type="application/json",
+        )
+
+        response = client.post(
+            f"/api/v1.0/mail-domains/{access.domain.slug}/mailboxes/",
+            mailbox_data,
+            format="json",
+        )
+        assert response.status_code == status.HTTP_201_CREATED
+
+    # Logger
+    assert not mock_error.called
+    assert mock_info.call_count == 3
+    assert mock_info.call_args_list[0][0] == (
+        "Token succesfully granted by mail-provisioning API.",
+    )
+    assert mock_info.call_args_list[1][0] == (
+        "Mailbox successfully created on domain %s",
+        access.domain.name,
+    )