When updating mail notifications during `mail.mail._send()`,

a `SerializationFailure` raised while flushing the notification recordset leaves the current transaction in an aborted state.

As `_send()` continues handling the exception, accessing fields:
 - https://github.com/odoo/odoo/blob/127f1316540ec6cc6880ea3515e6923ba3903bc7/addons/mail/models/mail_mail.py#L816

So, any subsequent SQL query fails with

`InFailedSqlTransaction`, masking the original concurrency error.

Avoid accesing to `mail.message_id` with aborted cursor, preserving the original `SerializationFailure`.

A regression test is added to simulate a concurrency failure during

`flush_recordset()` and verify that the cursor is no longer used dirty

The logger for the unittest without the fix is the following:

```log
During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "odoo/addons/mail/models/mail_mail.py", line 719, in _send
    notifs.flush_recordset(['notification_status', 'failure_type', 'failure_reason'])
  File "<string>", line 3, in flush_recordset
  File "unittest/mock.py", line 1139, in __call__
    return self._mock_call(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "unittest/mock.py", line 1143, in _mock_call
    return self._execute_mock_call(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "unittest/mock.py", line 1204, in _execute_mock_call
    result = effect(*args, **kwargs)
             ^^^^^^^^^^^^^^^^^^^^^^^
  File "odoo/addons/test_mail/tests/test_message_post_concurrent.py", line 93, in mocked_mail_notification_flush_recordset
    return original_flush_recordset(self, *vals, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "odoo/odoo/models.py", line 6788, in flush_recordset
    self._flush(fnames)
  File "odoo/odoo/models.py", line 6852, in _flush
    model.browse(some_ids)._write_multi(vals_list)
  File "odoo/odoo/models.py", line 4938, in _write_multi
    self.env.execute_query(SQL(
  File "odoo/odoo/api.py", line 993, in execute_query
    self.cr.execute(query)
  File "odoo/odoo/sql_db.py", line 371, in execute
    res = self._obj.execute(query, params)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
psycopg2.errors.SerializationFailure: could not serialize access due to concurrent update

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "odoo/addons/test_mail/tests/test_message_post_concurrent.py", line 107, in test_mail_send_dirty_cursor
    mails.send()
  File "odoo/addons/mail/models/mail_mail.py", line 652, in send
    self.browse(batch_ids)._send(
  File "odoo/addons/mail/models/mail_mail.py", line 818, in _send
    mail.id, mail.message_id)
             ^^^^^^^^^^^^^^^
  File "odoo/odoo/fields.py", line 1309, in __get__
    self.compute_value(recs)
  File "odoo/odoo/fields.py", line 1491, in compute_value
    records._compute_field_value(self)
  File "odoo/odoo/models.py", line 5302, in _compute_field_value
    fields.determine(field.compute, self)
  File "odoo/odoo/fields.py", line 113, in determine
    return needle(records, *args)
           ^^^^^^^^^^^^^^^^^^^^^^
  File "odoo/odoo/fields.py", line 710, in _compute_related
    record[self.name] = self._process_related(value[self.related_field.name], record.env)
                                              ~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^
  File "odoo/odoo/models.py", line 7083, in __getitem__
    return self._fields[key].__get__(self)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "odoo/odoo/fields.py", line 1272, in __get__
    recs._fetch_field(self)
  File "odoo/odoo/models.py", line 4120, in _fetch_field
    self.fetch(fnames)
  File "odoo/addons/mail/models/mail_message.py", line 756, in fetch
    return super().fetch(field_names)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "odoo/odoo/models.py", line 4158, in fetch
    fetched = self._fetch_query(query, fields_to_fetch)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "odoo/odoo/models.py", line 4245, in _fetch_query
    rows = self.env.execute_query(query.select(*sql_terms))
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "odoo/odoo/api.py", line 993, in execute_query
    self.cr.execute(query)
  File "odoo/odoo/sql_db.py", line 371, in execute
    res = self._obj.execute(query, params)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
psycopg2.errors.InFailedSqlTransaction: current transaction is aborted, commands ignored until end of transaction block
```

Real error in production:

```log
2023-04-15 10:43:14,978 106451 ERROR my_db odoo.sql_db: bad query: UPDATE "mail_notification" SET "failure_reason" = "__tmp"."failure_reason"::text, "failure_type" = "__tmp"."failure_type"::VARCHAR, "notification_status" = "__tmp"."notification_status"::VARCHAR FROM (VALUES (4426629, 'Error without exception. Probably due to concurrent access update of notification records. Please see with an administrator.', 'unknown', 'exception')) AS "__tmp"("id", "failure_reason", "failure_type", "notification_status") WHERE "mail_notification"."id" = "__tmp"."id" ERROR: could not serialize access due to concurrent update
```

```log
2023-04-14 10:43:14,978 106451 ERROR my_db odoo.sql_db: bad query: UPDATE "mail_mail" SET "failure_reason"='Error without exception. Probably due do sending an email without computed recipients.',"headers"='{''X-SMTPAPI'': ''{"ip_pool": "Transactional"}'', ''X-Odoo-Objects'': ''sale.order-1436960''}',"state"='exception',"write_uid"=1,"write_date"=(now() at time zone 'UTC') WHERE id IN (2548540)
ERROR: current transaction is aborted, commands ignored until end of transaction block
```

Description of the issue/feature this PR addresses:

Current behavior before PR:

Desired behavior after PR is merged:


# UPDATE 2026-07-22

The reviewer requested to remove the large docstring

For record, the docstring was

```python
    """Reproduces a concurrency scenario where `mail_mail._send()` fails with a PSQL SerializationFailure after
        flushing `mail.notification` records. After such a failure, the cursor is left in an aborted
        (`InFailedSqlTransaction`) state, so any further SQL access (e.g. reading `mail.message_id` like
        https://github.com/odoo/odoo/blob/127f1316540ec6cc68/addons/mail/models/mail_mail.py#L816)
        would raise a new error masking the original SerializationFailure.

        Setup:
        - Uses a separate `cursor()` to create and commit a message with its `mail.mail` and `mail.notification`
        records, so they are visible to a second, concurrent transaction.

        Concurrency simulation:
        - `MailNotification.flush_recordset` is patched so that, right before the real flush runs, a second cursor
        updates the same `mail.notification` records (`failure_reason`). This forces PSQL to raise a
        SerializationFailure when the original transaction tries to flush those rows.

        Assertions:
        - `SerializationFailure` is raised confirming the concurrency conflict.
        - `mail_mail._send()` logs the expected error message containing the mail `id` and `message-id`

        Cleanup: created records are unlinked in `finally`
        """
```

# UPDATE 2026-07-23

The reviewer requested to remove the unittest

For record, the unittest was

```diff
diff --git a/addons/test_mail/tests/test_message_post.py b/addons/test_mail/tests/test_message_post.py
index 53dd5b9eec52..46a3958a5bff 100644
--- a/addons/test_mail/tests/test_message_post.py
+++ b/addons/test_mail/tests/test_message_post.py
@@ -7,17 +7,21 @@ from datetime import datetime, timedelta
 from freezegun import freeze_time
 from itertools import product
 from markupsafe import escape, Markup
+from psycopg2.errorcodes import SERIALIZATION_FAILURE as SERIALIZATION_FAILURE_CODE
+from psycopg2.errors import SerializationFailure
 from unittest.mock import patch
 
-from odoo import tools
+from odoo import SUPERUSER_ID, api, tools
 from odoo.addons.base.tests.test_ir_cron import CronMixinCase
-from odoo.addons.mail.tests.common import mail_new_test_user, MailCommon
+from odoo.addons.mail.models.mail_notification import MailNotification
+from odoo.addons.mail.tests.common import mail_new_test_user, MailCommon, MockEmail
 from odoo.addons.test_mail.data.test_mail_data import MAIL_TEMPLATE_PLAINTEXT
 from odoo.addons.test_mail.models.test_mail_models import MailTestSimple
 from odoo.addons.test_mail.tests.common import TestRecipients
 from odoo.api import call_kw
 from odoo.exceptions import AccessError
-from odoo.tests import tagged
+from odoo.modules.registry import Registry
+from odoo.tests import TransactionCase, get_db_name, tagged
 from odoo.tools import mute_logger, formataddr
 from odoo.tests.common import users
 
@@ -2244,3 +2248,49 @@ class TestMessagePostLang(MailCommon, TestRecipients):
                                     self.assertIn('html lang="es_ES"', email['body'])
                                 else:
                                     self.assertIn('html lang="en_US"', email['body'])
+
+
+@tagged('database_breaking')
+class TestMessagePostConcurrent(MockEmail, TransactionCase):
+    """Mail concurrency edge cases that require real, separately committed transactions
+    instead of the usual rollback-based TransactionCase isolation.
+    """
+
+    def test_mail_send_dirty_cursor(self):
+        """Reproduces SerializationFailure `mail_mail._send()` fails,
+        the cursor is left in an aborted state, so any further SQL access would raise a new error
+        (e.g. reading `mail.message_id` like
+        https://github.com/odoo/odoo/blob/127f1316540ec6cc68/addons/mail/models/mail_mail.py#L816)
+        """
+        original_flush_recordset = MailNotification.flush_recordset
+
+        def mocked_mail_notification_flush_recordset(self, *args, **kwargs):
+            with Registry(get_db_name()).cursor() as cr:
+                cr.execute('UPDATE mail_notification SET failure_reason = %s WHERE id IN %s', ('Forced Concurrent Update', tuple(self.ids)))
+            return original_flush_recordset(self, *args, **kwargs)
+
+        recs2unlink = []
+        with Registry(get_db_name()).cursor() as cr:
+            env = api.Environment(cr, SUPERUSER_ID, {})
+            partner = env.ref('base.user_admin').partner_id
+            try:
+                message = partner.message_post(body='Hello', message_type='comment', partner_ids=[partner.id], mail_auto_delete=False, force_send=False)
+                notifs = env['mail.notification'].search([('notification_type', '=', 'email'), ('mail_mail_id', 'in', message.mail_ids.ids)])
+                self.assertTrue(notifs)
+                mails = message.mail_ids
+                recs2unlink.extend([notifs, mails, message])
+                cr.commit()
+
+                mails = self.env[mails._name].browse(mails.ids)
+                with (
+                    mute_logger('odoo.sql_db'), self.assertRaises(SerializationFailure) as exc, self.mock_mail_gateway(),
+                    patch(f'{MailNotification.__module__}.{MailNotification.__name__}.flush_recordset', autospec=True, side_effect=mocked_mail_notification_flush_recordset),
+                    self.assertLogs('odoo.addons.mail.models.mail_mail', level='ERROR') as log_capture,
+                ):
+                    mails.send()
+            finally:
+                for rec2unlink in recs2unlink:
+                    env[rec2unlink._name].browse(rec2unlink.ids).unlink()
+
+            self.assertEqual(exc.exception.pgcode, SERIALIZATION_FAILURE_CODE)
+            self.assertIn(f'Exception while processing mail with ID {mails.id} and Msg-Id \'{mails.message_id}\'.', [record.message for record in log_capture.records])

```

---
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Forward-Port-Of: odoo/odoo#279897
Forward-Port-Of: odoo/odoo#274089