diff --git a/addons/hr_expense/views/hr_expense_views.xml b/addons/hr_expense/views/hr_expense_views.xml
index c22586eb837..7a046cccd42 100644
--- a/addons/hr_expense/views/hr_expense_views.xml
+++ b/addons/hr_expense/views/hr_expense_views.xml
@@ -71,7 +71,6 @@
                     <field name="total_amount_company" optional="show" sum="Total Company Currency" widget='monetary' options="{'currency_field': 'company_currency_id'}" decoration-bf="True"/>
                     <field name="total_amount" optional="hide" decoration-bf="True" groups="base.group_multi_currency"/>
                     <field name="currency_id" optional="hide" groups="base.group_multi_currency"/>
-                    <field name="message_unread" invisible="1"/>
                     <field name="state" optional="show" readonly="1" decoration-info="state == 'draft'" decoration-success="state in ['reported', 'approved', 'done']" decoration-danger="state in 'refused'" widget="badge"/>
                 </tree>
             </field>
@@ -632,7 +631,6 @@
                     <field name="journal_id" optional="hide"/>
                     <field name="state" optional="show" decoration-info="state == 'draft'" decoration-success="state in ['submit', 'approve', 'post', 'done']" decoration-danger="state == 'cancel'" widget="badge"/>
                     <field name="payment_state" optional="show" decoration-info="payment_state in ('partial','in_payment')" decoration-success="payment_state == 'paid'" decoration-danger="payment_state in ('reversed','not_paid')" widget="badge"/>
-                    <field name="message_unread" invisible="1"/>
                 </tree>
             </field>
         </record>
@@ -762,8 +760,7 @@
                                     <field name="reference" optional="hide" readonly="True"/>
                                     <field name="analytic_account_id" optional="show" domain="['|', ('company_id', '=', parent.company_id), ('company_id', '=', False)]" groups="analytic.group_analytic_accounting"/>
                                     <field name="analytic_tag_ids" optional="hide" widget="many2many_tags" groups="analytic.group_analytic_tags"/>
-                                    <field name="account_id" optional="hide"/>
-                                    <field name="message_unread" invisible="1"/>
+                                    <field name="account_id" optional="hide" readonly="True"/>
                                     <button name="action_get_attachment_view" type="object" icon="fa-paperclip" aria-label="View Attachments" title="View Attachments" class="float-right pr-0" readonly="True"/>
                                     <field name="attachment_number" class="text-right pl-0 pr-4" width="1" nolabel="1"/>
                                     <field name="product_has_cost" invisible="True"/>
diff --git a/addons/mail/__manifest__.py b/addons/mail/__manifest__.py
index d5b0f118b71..a87b132c357 100644
--- a/addons/mail/__manifest__.py
+++ b/addons/mail/__manifest__.py
@@ -2,7 +2,7 @@
 
 {
     'name': 'Discuss',
-    'version': '1.7',
+    'version': '1.8',
     'category': 'Productivity/Discuss',
     'sequence': 145,
     'summary': 'Chat, mail gateway and private channels',
diff --git a/addons/mail/models/mail_channel.py b/addons/mail/models/mail_channel.py
index 07bd82af11f..322ba2c8f98 100644
--- a/addons/mail/models/mail_channel.py
+++ b/addons/mail/models/mail_channel.py
@@ -770,11 +770,10 @@ class Channel(models.Model):
             # find the channel partner state, if logged user
             if self.env.user and self.env.user.partner_id:
                 info['message_needaction_counter'] = channel.message_needaction_counter
-                info['message_unread_counter'] = channel.message_unread_counter
-                partner_channel = member_of_current_user_by_channel.get(channel, self.env['mail.channel.partner'])
+                partner_channel = member_of_current_user_by_channel.get(channel, self.env['mail.channel.partner']).with_prefetch([m.id for m in member_of_current_user_by_channel.values()])
                 if partner_channel:
-                    partner_channel = partner_channel[0]
                     info['state'] = partner_channel.fold_state or 'open'
+                    info['message_unread_counter'] = partner_channel.message_unread_counter
                     info['is_minimized'] = partner_channel.is_minimized
                     info['seen_message_id'] = partner_channel.seen_message_id.id
                     info['custom_channel_name'] = partner_channel.custom_channel_name
diff --git a/addons/mail/models/mail_channel_partner.py b/addons/mail/models/mail_channel_partner.py
index 6711e7c7a6c..38b0476c218 100644
--- a/addons/mail/models/mail_channel_partner.py
+++ b/addons/mail/models/mail_channel_partner.py
@@ -23,6 +23,7 @@ class ChannelPartner(models.Model):
     custom_channel_name = fields.Char('Custom channel name')
     fetched_message_id = fields.Many2one('mail.message', string='Last Fetched')
     seen_message_id = fields.Many2one('mail.message', string='Last Seen')
+    message_unread_counter = fields.Integer('Unread Messages Counter', compute='_compute_message_unread', compute_sudo=True, help='Number of unread messages')
     fold_state = fields.Selection([('open', 'Open'), ('folded', 'Folded'), ('closed', 'Closed')], string='Conversation Fold State', default='open')
     is_minimized = fields.Boolean("Conversation is minimized")
     is_pinned = fields.Boolean("Is pinned on the interface", default=True)
@@ -31,6 +32,28 @@ class ChannelPartner(models.Model):
     rtc_session_ids = fields.One2many(string="RTC Sessions", comodel_name='mail.channel.rtc.session', inverse_name='channel_partner_id')
     rtc_inviting_session_id = fields.Many2one('mail.channel.rtc.session', string='Ringing session')
 
+    @api.depends('channel_id.message_ids', 'seen_message_id')
+    def _compute_message_unread(self):
+        self.flush()
+        self.env.cr.execute("""
+                 SELECT count(mail_message.id) AS count,
+                        mail_channel_partner.id
+                   FROM mail_message
+             INNER JOIN mail_channel_partner
+                     ON mail_channel_partner.channel_id = mail_message.res_id
+                  WHERE mail_message.model = 'mail.channel'
+                    AND mail_message.message_type NOT IN ('notification', 'user_notification')
+                    AND (
+                        mail_message.id > mail_channel_partner.seen_message_id
+                     OR mail_channel_partner.seen_message_id IS NULL
+                    )
+                    AND mail_channel_partner.id IN %(ids)s
+               GROUP BY mail_channel_partner.id
+        """, {'ids': tuple(self.ids)})
+        unread_counter_by_channel_partner = {res['id']: res['count'] for res in self.env.cr.dictfetchall()}
+        for channel_partner in self:
+            channel_partner.message_unread_counter = unread_counter_by_channel_partner.get(channel_partner.id)
+
     def name_get(self):
         return [(record.id, record.partner_id.name or record.guest_id.name) for record in self]
 
diff --git a/addons/mail/models/mail_message.py b/addons/mail/models/mail_message.py
index a0403666a97..1d7189a83e8 100644
--- a/addons/mail/models/mail_message.py
+++ b/addons/mail/models/mail_message.py
@@ -1088,8 +1088,6 @@ class Message(models.Model):
             if issubclass(self.pool[model], self.pool['mail.thread']):
                 self.env[model].invalidate_cache(fnames=[
                     'message_ids',
-                    'message_unread',
-                    'message_unread_counter',
                     'message_needaction',
                     'message_needaction_counter',
                 ], ids=[res_id])
diff --git a/addons/mail/models/mail_thread.py b/addons/mail/models/mail_thread.py
index 7b82d1006bf..ef2fe1c7631 100644
--- a/addons/mail/models/mail_thread.py
+++ b/addons/mail/models/mail_thread.py
@@ -89,12 +89,6 @@ class MailThread(models.AbstractModel):
         'mail.message', 'res_id', string='Messages',
         domain=lambda self: [('message_type', '!=', 'user_notification')], auto_join=True)
     has_message = fields.Boolean(compute="_compute_has_message", search="_search_has_message", store=False)
-    message_unread = fields.Boolean(
-        'Unread Messages', compute='_compute_message_unread',
-        help="If checked, new messages require your attention.")
-    message_unread_counter = fields.Integer(
-        'Unread Messages Counter', compute='_compute_message_unread',
-        help="Number of unread messages")
     message_needaction = fields.Boolean(
         'Action Needed',
         compute='_compute_message_needaction', search='_search_message_needaction',
@@ -176,27 +170,6 @@ class MailThread(models.AbstractModel):
             operator_new = 'not inselect'
         return [('id', operator_new, ("SELECT res_id FROM mail_message WHERE model=%s", [self._name]))]
 
-    def _compute_message_unread(self):
-        partner_id = self.env.user.partner_id.id
-        res = dict.fromkeys(self.ids, 0)
-        if self.ids:
-            # search for unread messages, directly in SQL to improve performances
-            self._cr.execute(""" SELECT msg.res_id FROM mail_message msg
-                                 RIGHT JOIN mail_channel_partner cp
-                                 ON (cp.channel_id = msg.res_id AND cp.partner_id = %s AND
-                                    (cp.seen_message_id IS NULL OR cp.seen_message_id < msg.id))
-                                 WHERE msg.model = %s AND msg.res_id = ANY(%s) AND
-                                        msg.message_type != 'user_notification' AND
-                                       (msg.author_id IS NULL OR msg.author_id != %s) AND
-                                       (msg.message_type not in ('notification', 'user_notification') OR msg.model != 'mail.channel')""",
-                             (partner_id, self._name, list(self.ids), partner_id,))
-            for result in self._cr.fetchall():
-                res[result[0]] += 1
-
-        for record in self:
-            record.message_unread_counter = res.get(record._origin.id, 0)
-            record.message_unread = bool(record.message_unread_counter)
-
     def _compute_message_needaction(self):
         res = dict.fromkeys(self.ids, 0)
         if self.ids:
diff --git a/addons/mail/static/tests/helpers/model_definitions_setup.js b/addons/mail/static/tests/helpers/model_definitions_setup.js
index b80e51a6544..2097d2cbd76 100644
--- a/addons/mail/static/tests/helpers/model_definitions_setup.js
+++ b/addons/mail/static/tests/helpers/model_definitions_setup.js
@@ -53,6 +53,7 @@ insertModelFields('mail.channel', {
         string: "Members",
         type: 'many2many'
     },
+    message_unread_counter: { string: 'Unread counter', type: 'integer' },
     seen_message_id:  { relation: 'mail.message', string: "Last Seen", type: 'many2one' },
     state: { default: 'open', string: "FoldState", type: "char" },
     uuid: { default: () => _.uniqueId('mail.channel_uuid-') },
diff --git a/addons/mail/tests/test_mail_channel_partner.py b/addons/mail/tests/test_mail_channel_partner.py
index ab89753d124..8f6e8a66424 100644
--- a/addons/mail/tests/test_mail_channel_partner.py
+++ b/addons/mail/tests/test_mail_channel_partner.py
@@ -30,6 +30,10 @@ class TestMailChannelMembers(MailCommon):
             cls.env, login='user_2',
             name='User 2',
             groups='base.group_user,mail.secret_group')
+        cls.user_3 = mail_new_test_user(
+            cls.env, login='user_3',
+            name='User 3',
+            groups='base.group_user,mail.secret_group')
         cls.user_portal = mail_new_test_user(
             cls.env, login='user_portal',
             name='User Portal',
@@ -222,3 +226,54 @@ class TestMailChannelMembers(MailCommon):
             self.public_channel.with_user(self.user_portal).add_members(self.user_portal.partner_id.ids)
         with self.assertRaises(AccessError):
             self.public_channel.with_user(self.user_public).add_members(self.user_public.partner_id.ids)
+
+    # ------------------------------------------------------------
+    # UNREAD COUNTER TESTS
+    # ------------------------------------------------------------
+
+    def test_unread_counter_with_message_post(self):
+        channel_as_user_1 = self.env['mail.channel'].with_user(self.user_1).create({
+            'name': 'Secret channel',
+            'public': 'public',
+            'channel_type': 'channel',
+        })
+        channel_as_user_1.with_user(self.user_1).add_members(self.user_1.partner_id.ids)
+        channel_as_user_1.with_user(self.user_1).add_members(self.user_2.partner_id.ids)
+        channel_1_rel_user_2 = self.env['mail.channel.partner'].search([
+            ('channel_id', '=', channel_as_user_1.id),
+            ('partner_id', '=', self.user_2.partner_id.id)
+        ])
+        self.assertEqual(channel_1_rel_user_2.message_unread_counter, 0, "should not have unread message initially as notification type is ignored")
+
+        channel_as_user_1.message_post(body='Test', message_type='comment', subtype_xmlid='mail.mt_comment')
+        channel_1_rel_user_2 = self.env['mail.channel.partner'].search([
+            ('channel_id', '=', channel_as_user_1.id),
+            ('partner_id', '=', self.user_2.partner_id.id)
+        ])
+        self.assertEqual(channel_1_rel_user_2.message_unread_counter, 1, "should have 1 unread message after someone else posted a message")
+
+    def test_unread_counter_with_message_post_multi_channel(self):
+        channel_1_as_user_1 = self.env['mail.channel'].with_user(self.user_1).create({
+            'name': 'wololo channel',
+            'public': 'public',
+            'channel_type': 'channel',
+        })
+        channel_2_as_user_2 = self.env['mail.channel'].with_user(self.user_2).create({
+            'name': 'walala channel',
+            'public': 'public',
+            'channel_type': 'channel',
+        })
+        channel_1_as_user_1.add_members(self.user_2.partner_id.ids)
+        channel_2_as_user_2.add_members(self.user_1.partner_id.ids)
+        channel_2_as_user_2.add_members(self.user_3.partner_id.ids)
+        channel_1_as_user_1.message_post(body='Test', message_type='comment', subtype_xmlid='mail.mt_comment')
+        channel_1_as_user_1.message_post(body='Test 2', message_type='comment', subtype_xmlid='mail.mt_comment')
+        channel_2_as_user_2.message_post(body='Test', message_type='comment', subtype_xmlid='mail.mt_comment')
+        members = self.env['mail.channel.partner'].search([('channel_id', 'in', (channel_1_as_user_1 + channel_2_as_user_2).ids)], order="id")
+        self.assertEqual(members.mapped('message_unread_counter'), [
+            0,  # channel 1 user 1: posted last message
+            0,  # channel 2 user 2: posted last message
+            2,  # channel 1 user 2: received 2 messages (from message post)
+            1,  # channel 2 user 1: received 1 message (from message post)
+            1,  # channel 2 user 3: received 1 message (from message post)
+        ])
diff --git a/addons/purchase/views/purchase_views.xml b/addons/purchase/views/purchase_views.xml
index d1f2e4e599a..15739b3e612 100644
--- a/addons/purchase/views/purchase_views.xml
+++ b/addons/purchase/views/purchase_views.xml
@@ -516,10 +516,9 @@
             <field name="model">purchase.order</field>
             <field name="priority" eval="1"/>
             <field name="arch" type="xml">
-                <tree string="Purchase Order" decoration-bf="message_unread==True"
+                <tree string="Purchase Order"
                       decoration-muted="state=='cancel'" sample="1">
                     <field name="priority" optional="show" widget="priority" nolabel="1"/>
-                    <field name="message_unread" invisible="1"/>
                     <field name="partner_ref" optional="hide"/>
                     <field name="name" string="Reference" readonly="1" decoration-info="state in ('draft','sent')"/>
                     <field name="date_order" invisible="not context.get('quotation_only', False)" optional="show"/>
@@ -548,13 +547,12 @@
             <field name="priority" eval="10"/>
             <field name="arch" type="xml">
                 <tree string="Purchase Order" decoration-info="state in ['draft', 'sent']"
-                decoration-muted="state == 'cancel'" decoration-bf="message_unread==True"
+                decoration-muted="state == 'cancel'"
                 class="o_purchase_order" js_class="purchase_list_dashboard" sample="1">
                     <header>
                         <button name="action_create_invoice" type="object" string="Create Bills"/>
                     </header>
                     <field name="priority" optional="show" widget="priority" nolabel="1"/>
-                    <field name="message_unread" invisible="1"/>
                     <field name="partner_ref" optional="hide"/>
                     <field name="name" string="Reference" readonly="1" decoration-bf="1"/>
                     <field name="date_approve" invisible="context.get('quotation_only', False)" optional="show"/>
@@ -581,8 +579,7 @@
             <field name="name">purchase.order.view.tree</field>
             <field name="model">purchase.order</field>
             <field name="arch" type="xml">
-                <tree decoration-bf="message_unread==True"
-                    decoration-muted="state == 'cancel'"
+                <tree decoration-muted="state == 'cancel'"
                     decoration-info="invoice_status == 'to invoice'"
                     string="Purchase Order"
                     class="o_purchase_order"
@@ -591,7 +588,6 @@
                         <button name="action_create_invoice" type="object" string="Create Bills"/>
                     </header>
                     <field name="priority" optional="show" widget="priority" nolabel="1"/>
-                    <field name="message_unread" invisible="1"/>
                     <field name="partner_ref" optional="hide"/>
                     <field name="name" string="Reference" readonly="1" decoration-bf="1" decoration-info="state in ('draft','sent')"/>
                     <field name="date_approve" widget="date" invisible="context.get('quotation_only', False)" optional="show"/>
diff --git a/addons/test_discuss_full/tests/test_performance.py b/addons/test_discuss_full/tests/test_performance.py
index 6bd8230774c..5e74ef874ee 100644
--- a/addons/test_discuss_full/tests/test_performance.py
+++ b/addons/test_discuss_full/tests/test_performance.py
@@ -99,7 +99,7 @@ class TestDiscussFullPerformance(TransactionCase):
         self.maxDiff = None
         self.users[0].flush()
         self.users[0].invalidate_cache()
-        with self.assertQueryCount(emp=85):  # ent: 84
+        with self.assertQueryCount(emp=86):
             init_messaging = self.users[0].with_user(self.users[0])._init_messaging()
 
         self.assertEqual(init_messaging, {