diff --git a/addons/mail_group/models/mail_group.py b/addons/mail_group/models/mail_group.py
index 19d3ccab7b9..c792c8409bc 100644
--- a/addons/mail_group/models/mail_group.py
+++ b/addons/mail_group/models/mail_group.py
@@ -18,6 +18,7 @@ from odoo.tools import email_normalize, hmac, generate_tracking_message_id
 
 _logger = logging.getLogger(__name__)
 
+# TODO remove me master
 GROUP_SEND_BATCH_SIZE = 500
 
 
@@ -407,7 +408,6 @@ class MailGroup(models.Model):
         base_url = self.get_base_url()
         body = self.env['mail.render.mixin']._replace_local_links(message.body)
         access_token = self._generate_group_access_token()
-        mail_values = []
 
         # Email added in a dict to be sure to send only once the email to each address
         member_emails = {
@@ -415,7 +415,9 @@ class MailGroup(models.Model):
             for member in self.member_ids
         }
 
-        for batch_email_member in tools.split_every(GROUP_SEND_BATCH_SIZE, member_emails.items()):
+        batch_size = int(self.env['ir.config_parameter'].sudo().get_param('mail.session.batch.size', GROUP_SEND_BATCH_SIZE))
+        for batch_email_member in tools.split_every(batch_size, member_emails.items()):
+            mail_values = []
             for email_member_normalized, email_member in batch_email_member:
                 if email_member_normalized == message.email_from_normalized:
                     # Do not send the email to their author
diff --git a/addons/mail_group/tests/test_mail_group_message.py b/addons/mail_group/tests/test_mail_group_message.py
index bf3af153436..8db92915b72 100644
--- a/addons/mail_group/tests/test_mail_group_message.py
+++ b/addons/mail_group/tests/test_mail_group_message.py
@@ -8,6 +8,42 @@ from odoo.tools import mute_logger
 
 
 class TestMailGroupMessage(TestMailListCommon):
+
+    def test_batch_send(self):
+        """Test that when someone sends an email to a large group that it is
+        delivered exactly to those people"""
+        self.test_group.write({
+            'access_mode': 'members',
+            'alias_contact': 'followers',
+            'moderation': False,
+        })
+        self.test_group.member_ids.unlink()
+
+        for num in range(42):
+            self.env['mail.group.member'].create({
+                'email': f'emu-{num}@example.com',
+                'mail_group_id': self.test_group.id,
+            })
+
+        self.assertEqual(len(self.test_group.member_ids), 42)
+
+        # force a batch split with a low limit
+        self.env['ir.config_parameter'].sudo().set_param('mail.session.batch.size', 10)
+
+        with self.mock_mail_gateway():
+            self.format_and_process(
+                GROUP_TEMPLATE, self.test_group.member_ids[0].email,
+                self.test_group.alias_id.display_name,
+                subject='Never Surrender', msg_id='<glory.to.the.hypnotoad@localhost>', target_model='mail.group')
+
+        message = self.env['mail.group.message'].search([('mail_message_id.message_id', '=', '<glory.to.the.hypnotoad@localhost>')])
+        self.assertEqual(message.subject, 'Never Surrender', 'Should have created a <mail.group.message>')
+
+        mails = self.env['mail.mail'].search([('mail_message_id', '=', message.mail_message_id.id)])
+
+        # 42 -1 as the sender doesn't get an email
+        self.assertEqual(len(mails), 41, 'Should have send one and only one email per recipient')
+
     @mute_logger('odoo.addons.mail.models.mail_thread', 'odoo.addons.mail_group.models.mail_group_message')
     def test_email_duplicated(self):
         """ Test gateway does not accept two times same incoming email """