diff --git a/addons/mail/models/mail_followers.py b/addons/mail/models/mail_followers.py
index 4040de72276..469ab1d747c 100644
--- a/addons/mail/models/mail_followers.py
+++ b/addons/mail/models/mail_followers.py
@@ -198,6 +198,7 @@ GROUP BY fol.id%s""" % (
 
           * skip: simply skip existing followers, do not touch them;
           * force: update existing with given subtypes only;
+          * replace: replace existing with nex subtypes (like force without old / new follower);
           * update: gives an update dict allowing to add missing subtypes (no subtype removal);
         """
         _res_ids = res_ids or [0]
@@ -224,11 +225,14 @@ GROUP BY fol.id%s""" % (
                         'partner_id': partner_id,
                         'subtype_ids': [(6, 0, partner_subtypes[partner_id])],
                     })
-                elif existing_policy == 'update':
+                elif existing_policy in ('replace', 'update'):
                     fol_id, sids = next(((key, val[3]) for key, val in data_fols.items() if val[0] == res_id and val[1] == partner_id), (False, []))
                     new_sids = set(partner_subtypes[partner_id]) - set(sids)
+                    old_sids = set(sids) - set(partner_subtypes[partner_id])
                     if fol_id and new_sids:
                         update[fol_id] = {'subtype_ids': [(4, sid) for sid in new_sids]}
+                    if fol_id and old_sids and existing_policy == 'replace':
+                        update[fol_id] = {'subtype_ids': [(3, sid) for sid in old_sids]}
             for channel_id in set(channel_ids or []):
                 if channel_id not in doc_cids[res_id]:
                     new.setdefault(res_id, list()).append({
@@ -236,10 +240,13 @@ GROUP BY fol.id%s""" % (
                         'channel_id': channel_id,
                         'subtype_ids': [(6, 0, channel_subtypes[channel_id])],
                     })
-                elif existing_policy == 'update':
+                elif existing_policy in ('replace', 'update'):
                     fol_id, sids = next(((key, val[3]) for key, val in data_fols.items() if val[0] == res_id and val[2] == channel_id), (False, []))
                     new_sids = set(channel_subtypes[channel_id]) - set(sids)
+                    old_sids = set(sids) - set(channel_subtypes[channel_id])
                     if fol_id and new_sids:
                         update[fol_id] = {'subtype_ids': [(4, sid) for sid in new_sids]}
+                    if fol_id and old_sids and existing_policy == 'replace':
+                        update[fol_id] = {'subtype_ids': [(3, sid) for sid in old_sids]}
 
         return new, update
diff --git a/addons/mail/models/mail_thread.py b/addons/mail/models/mail_thread.py
index 9af7ea554ef..f92b8006fc3 100644
--- a/addons/mail/models/mail_thread.py
+++ b/addons/mail/models/mail_thread.py
@@ -2082,7 +2082,7 @@ class MailThread(models.AbstractModel):
                 self._name, self.ids,
                 partner_ids, dict((pid, subtype_ids) for pid in partner_ids),
                 channel_ids, dict((cid, subtype_ids) for cid in channel_ids),
-                customer_ids=customer_ids, check_existing=True, existing_policy='force')
+                customer_ids=customer_ids, check_existing=True, existing_policy='replace')
 
         return True
 
diff --git a/addons/test_mail/tests/test_performance.py b/addons/test_mail/tests/test_performance.py
index 3ce8126440b..2b3442608c0 100644
--- a/addons/test_mail/tests/test_performance.py
+++ b/addons/test_mail/tests/test_performance.py
@@ -291,7 +291,7 @@ class TestAdvMailPerformance(TransactionCase):
         with self.assertQueryCount(admin=5, emp=5):  # test_mail only: 5 - 5
             record.message_subscribe(partner_ids=self.user_test.partner_id.ids, subtype_ids=subtype_ids)
 
-        with self.assertQueryCount(admin=12, emp=12):  # test_mail only: 12 - 12
+        with self.assertQueryCount(admin=1, emp=1):  # test_mail only: 1 - 1
             record.message_subscribe(partner_ids=self.user_test.partner_id.ids, subtype_ids=subtype_ids)
 
 
@@ -449,7 +449,7 @@ class TestHeavyMailPerformance(TransactionCase):
         self.assertEqual(rec.message_channel_ids, self.channel)
 
         # subscribe existing and new followers with force=True, meaning all will have the same subtypes
-        with self.assertQueryCount(admin=42, emp=42):  # test_mail only: 42 - 42
+        with self.assertQueryCount(admin=13, emp=13):  # test_mail only: 13 - 13
             rec.message_subscribe(
                 partner_ids=pids,
                 channel_ids=cids,