diff --git a/addons/mail/controllers/__init__.py b/addons/mail/controllers/__init__.py
index 10fb0480208..0ae7eeab10f 100644
--- a/addons/mail/controllers/__init__.py
+++ b/addons/mail/controllers/__init__.py
@@ -1,5 +1,7 @@
 # -*- coding: utf-8 -*
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 
-from . import discuss
 from . import mail
+
+# after mail specifically as discuss module depends on mail
+from . import discuss
diff --git a/addons/mail/models/__init__.py b/addons/mail/models/__init__.py
index 80c11ba7681..b520bdcd34e 100644
--- a/addons/mail/models/__init__.py
+++ b/addons/mail/models/__init__.py
@@ -34,10 +34,6 @@ from . import mail_tracking_value
 from . import mail_template
 
 # discuss
-from . import discuss_channel_member
-from . import discuss_channel_rtc_session
-from . import discuss_channel
-from . import mail_guest
 from . import mail_ice_server
 from . import mail_shortcode
 from . import res_users_settings
@@ -55,10 +51,13 @@ from . import ir_model
 from . import ir_model_fields
 from . import ir_ui_view
 from . import ir_qweb
-from . import ir_websocket
 from . import res_company
 from . import res_config_settings
-from . import res_partner
 from . import res_users
-from . import res_groups
 from . import update
+
+# after mail specifically as discuss module depends on mail
+from . import discuss
+
+# discuss_channel_member must be loaded first
+from . import res_partner
diff --git a/addons/mail/models/discuss/__init__.py b/addons/mail/models/discuss/__init__.py
new file mode 100644
index 00000000000..3dd130faf9d
--- /dev/null
+++ b/addons/mail/models/discuss/__init__.py
@@ -0,0 +1,17 @@
+# Part of Odoo. See LICENSE file for full copyright and licensing details.
+
+# mail
+from . import mail_message
+
+# discuss
+from . import discuss_channel_member
+from . import discuss_channel_rtc_session
+from . import discuss_channel
+from . import mail_guest
+
+# odoo models
+from . import ir_attachment
+from . import ir_websocket
+from . import res_groups
+from . import res_partner
+from . import res_users
diff --git a/addons/mail/models/discuss_channel.py b/addons/mail/models/discuss/discuss_channel.py
similarity index 99%
rename from addons/mail/models/discuss_channel.py
rename to addons/mail/models/discuss/discuss_channel.py
index 14ce2625372..d1438fb31d4 100644
--- a/addons/mail/models/discuss_channel.py
+++ b/addons/mail/models/discuss/discuss_channel.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 
 import base64
@@ -260,7 +259,7 @@ class Channel(models.Model):
             failing_channels = self.sudo().filtered(lambda channel: channel.channel_type != vals.get('channel_type'))
             if failing_channels:
                 raise UserError(_('Cannot change the channel type of: %(channel_names)s'), channel_names=', '.join(failing_channels.mapped('name')))
-        result = super(Channel, self).write(vals)
+        result = super().write(vals)
         if vals.get('group_ids'):
             self._subscribe_users_automatically()
         if 'image_128' in vals:
@@ -561,7 +560,7 @@ class Channel(models.Model):
 
     def _notify_thread(self, message, msg_vals=False, **kwargs):
         # link message to channel
-        rdata = super(Channel, self)._notify_thread(message, msg_vals=msg_vals, **kwargs)
+        rdata = super()._notify_thread(message, msg_vals=msg_vals, **kwargs)
 
         message_format_values = message.message_format()[0]
         bus_notifications = self._channel_message_notifications(message, message_format_values)
@@ -583,7 +582,7 @@ class Channel(models.Model):
         for p in partner:
             if p.message_bounce >= self.MAX_BOUNCE_LIMIT:
                 self._action_unfollow(p)
-        return super(Channel, self)._message_receive_bounce(email, partner)
+        return super()._message_receive_bounce(email, partner)
 
     def _message_compute_author(self, author_id=None, email_from=None, raise_on_email=True):
         return super()._message_compute_author(author_id=author_id, email_from=email_from, raise_on_email=False)
@@ -1163,7 +1162,7 @@ class Channel(models.Model):
 
     @api.model
     def get_mention_suggestions(self, search, limit=8):
-        """ Return 'limit'-first channels' id, name, channel_type and  authorizedGroupFullName fields such that the
+        """ Return 'limit'-first channels' id, name, channel_type and authorizedGroupFullName fields such that the
             name matches a 'search' string. Exclude channels of type chat (DM) and group.
         """
         domain = expression.AND([
diff --git a/addons/mail/models/discuss_channel_member.py b/addons/mail/models/discuss/discuss_channel_member.py
similarity index 100%
rename from addons/mail/models/discuss_channel_member.py
rename to addons/mail/models/discuss/discuss_channel_member.py
diff --git a/addons/mail/models/discuss_channel_rtc_session.py b/addons/mail/models/discuss/discuss_channel_rtc_session.py
similarity index 99%
rename from addons/mail/models/discuss_channel_rtc_session.py
rename to addons/mail/models/discuss/discuss_channel_rtc_session.py
index 88e25c39afe..d76133db806 100644
--- a/addons/mail/models/discuss_channel_rtc_session.py
+++ b/addons/mail/models/discuss/discuss_channel_rtc_session.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 
 from collections import defaultdict
diff --git a/addons/mail/models/discuss/ir_attachment.py b/addons/mail/models/discuss/ir_attachment.py
new file mode 100644
index 00000000000..c61cb4ae4ca
--- /dev/null
+++ b/addons/mail/models/discuss/ir_attachment.py
@@ -0,0 +1,16 @@
+# Part of Odoo. See LICENSE file for full copyright and licensing details.
+
+from odoo import models
+
+
+class IrAttachment(models.Model):
+    _inherit = "ir.attachment"
+
+    def _bus_notification_target(self):
+        self.ensure_one()
+        if self.res_model == "discuss.channel" and self.res_id:
+            return self.env["discuss.channel"].browse(self.res_id)
+        guest = self.env["mail.guest"]._get_guest_from_context()
+        if self.env.user._is_public() and guest:
+            return guest
+        return super()._bus_notification_target()
diff --git a/addons/mail/models/ir_websocket.py b/addons/mail/models/discuss/ir_websocket.py
similarity index 70%
rename from addons/mail/models/ir_websocket.py
rename to addons/mail/models/discuss/ir_websocket.py
index 8b5c99ac203..84ea5faf383 100644
--- a/addons/mail/models/ir_websocket.py
+++ b/addons/mail/models/discuss/ir_websocket.py
@@ -4,14 +4,16 @@ from odoo.addons.bus.websocket import wsrequest
 
 
 class IrWebsocket(models.AbstractModel):
-    _inherit = 'ir.websocket'
+    _inherit = "ir.websocket"
 
     def _get_im_status(self, data):
         im_status = super()._get_im_status(data)
-        if 'mail.guest' in data:
-            im_status['Guest'] = self.env['mail.guest'].sudo().with_context(active_test=False).search_read(
-                [('id', 'in', data['mail.guest'])],
-                ['im_status']
+        if "mail.guest" in data:
+            im_status["Guest"] = (
+                self.env["mail.guest"]
+                .sudo()
+                .with_context(active_test=False)
+                .search_read([("id", "in", data["mail.guest"])], ["im_status"])
             )
         return im_status
 
@@ -22,8 +24,8 @@ class IrWebsocket(models.AbstractModel):
         #  request.
         req = request or wsrequest
         channels = list(channels)  # do not alter original list
-        guest_sudo = self.env['mail.guest']._get_guest_from_request(req).sudo()
-        discuss_channels = self.env['discuss.channel']
+        guest_sudo = self.env["mail.guest"]._get_guest_from_request(req).sudo()
+        discuss_channels = self.env["discuss.channel"]
         if req.session.uid:
             discuss_channels = self.env.user.partner_id.channel_ids
         elif guest_sudo:
@@ -41,7 +43,11 @@ class IrWebsocket(models.AbstractModel):
             #  retrieve the current guest. Let's retrieve the proper
             #  request.
             req = request or wsrequest
-            guest_sudo = self.env['mail.guest']._get_guest_from_request(req).sudo()
+            guest_sudo = self.env["mail.guest"]._get_guest_from_request(req).sudo()
             if not guest_sudo:
                 return
-            guest_sudo.env['bus.presence'].update_presence(inactivity_period, identity_field='guest_id', identity_value=guest_sudo.id)
+            guest_sudo.env["bus.presence"].update_presence(
+                inactivity_period,
+                identity_field="guest_id",
+                identity_value=guest_sudo.id,
+            )
diff --git a/addons/mail/models/mail_guest.py b/addons/mail/models/discuss/mail_guest.py
similarity index 99%
rename from addons/mail/models/mail_guest.py
rename to addons/mail/models/discuss/mail_guest.py
index af37c40504a..f5465b2f225 100644
--- a/addons/mail/models/mail_guest.py
+++ b/addons/mail/models/discuss/mail_guest.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 
 import pytz
diff --git a/addons/mail/models/discuss/mail_message.py b/addons/mail/models/discuss/mail_message.py
new file mode 100644
index 00000000000..93c6cce3de9
--- /dev/null
+++ b/addons/mail/models/discuss/mail_message.py
@@ -0,0 +1,23 @@
+# Part of Odoo. See LICENSE file for full copyright and licensing details.
+
+from odoo import models
+
+
+class MailMessage(models.Model):
+    _inherit = "mail.message"
+
+    def _message_format_extras(self, format_reply):
+        self.ensure_one()
+        vals = super()._message_format_extras(format_reply)
+        if format_reply and self.model == "discuss.channel" and self.parent_id:
+            vals["parentMessage"] = self.parent_id.message_format(format_reply=False)[0]
+        return vals
+
+    def _bus_notification_target(self):
+        self.ensure_one()
+        if self.model == "discuss.channel" and self.res_id:
+            return self.env["discuss.channel"].browse(self.res_id)
+        guest = self.env["mail.guest"]._get_guest_from_context()
+        if self.env.user._is_public() and guest:
+            return guest
+        return super()._bus_notification_target()
diff --git a/addons/mail/models/discuss/res_groups.py b/addons/mail/models/discuss/res_groups.py
new file mode 100644
index 00000000000..745979d2127
--- /dev/null
+++ b/addons/mail/models/discuss/res_groups.py
@@ -0,0 +1,16 @@
+# Part of Odoo. See LICENSE file for full copyright and licensing details.
+
+from odoo import models
+
+
+class ResGroups(models.Model):
+    _inherit = "res.groups"
+
+    def write(self, vals):
+        res = super().write(vals)
+        if vals.get("users"):
+            # form: {'group_ids': [(3, 10), (3, 3), (4, 10), (4, 3)]} or {'group_ids': [(6, 0, [ids]}
+            user_ids = [command[1] for command in vals["users"] if command[0] == 4]
+            user_ids += [id for command in vals["users"] if command[0] == 6 for id in command[2]]
+            self.env["discuss.channel"].search([("group_ids", "in", self._ids)])._subscribe_users_automatically()
+        return res
diff --git a/addons/mail/models/discuss/res_partner.py b/addons/mail/models/discuss/res_partner.py
new file mode 100644
index 00000000000..cc84e89053b
--- /dev/null
+++ b/addons/mail/models/discuss/res_partner.py
@@ -0,0 +1,128 @@
+# Part of Odoo. See LICENSE file for full copyright and licensing details.
+
+from odoo import api, fields, models
+from odoo.osv import expression
+
+
+class ResPartner(models.Model):
+    _inherit = "res.partner"
+
+    channel_ids = fields.Many2many(
+        "discuss.channel",
+        "discuss_channel_member",
+        "partner_id",
+        "channel_id",
+        string="Channels",
+        copy=False,
+    )
+
+    def _get_channels_as_member(self):
+        """Returns the channels of the partner."""
+        self.ensure_one()
+        channels = self.env["discuss.channel"]
+        # get the channels and groups
+        channels |= self.env["discuss.channel"].search(
+            [
+                ("channel_type", "in", ("channel", "group")),
+                ("channel_partner_ids", "in", [self.id]),
+            ]
+        )
+        # get the pinned direct messages
+        channels |= self.env["discuss.channel"].search(
+            [
+                ("channel_type", "=", "chat"),
+                (
+                    "channel_member_ids",
+                    "in",
+                    self.env["discuss.channel.member"]
+                    .sudo()
+                    ._search(
+                        [
+                            ("partner_id", "=", self.id),
+                            ("is_pinned", "=", True),
+                        ]
+                    ),
+                ),
+            ]
+        )
+        return channels
+
+    @api.model
+    def search_for_channel_invite(self, search_term, channel_id=None, limit=30):
+        """Returns partners matching search_term that can be invited to a channel.
+        If the channel_id is specified, only partners that can actually be invited to the channel
+        are returned (not already members, and in accordance to the channel configuration).
+        """
+        domain = expression.AND(
+            [
+                expression.OR(
+                    [
+                        [("name", "ilike", search_term)],
+                        [("email", "ilike", search_term)],
+                    ]
+                ),
+                [("active", "=", True)],
+                [("type", "!=", "private")],
+                [("user_ids", "!=", False)],
+                [("user_ids.active", "=", True)],
+                [("user_ids.share", "=", False)],
+            ]
+        )
+        if channel_id:
+            channel = self.env["discuss.channel"].search([("id", "=", int(channel_id))])
+            domain = expression.AND([domain, [("channel_ids", "not in", channel.id)]])
+            if channel.group_public_id:
+                domain = expression.AND([domain, [("user_ids.groups_id", "in", channel.group_public_id.id)]])
+        query = self.env["res.partner"]._search(domain, order="name, id")
+        query.order = 'LOWER("res_partner"."name"), "res_partner"."id"'  # bypass lack of support for case insensitive order in search()
+        query.limit = int(limit)
+        return {
+            "count": self.env["res.partner"].search_count(domain),
+            "partners": list(self.env["res.partner"].browse(query).mail_partner_format().values()),
+        }
+
+    @api.model
+    def get_mention_suggestions_from_channel(self, channel_id, search, limit=8):
+        """Return 'limit'-first partners' such that the name or email matches a 'search' string.
+        Prioritize partners that are also (internal) users, and then extend the research to all partners.
+        Only members of the given channel are returned.
+        The return format is a list of partner data (as per returned by `mail_partner_format()`).
+        """
+        channel = self.env["discuss.channel"].search([("id", "=", channel_id)])
+        if not channel:
+            return []
+        domain = expression.AND(
+            [
+                self._get_mention_suggestions_domain(search),
+                [("channel_ids", "in", channel.id)],
+            ]
+        )
+        partners = self._search_mention_suggestions(domain, limit)
+        member_by_partner = {
+            member.partner_id: member
+            for member in self.env["discuss.channel.member"].search(
+                [
+                    ("channel_id", "=", channel.id),
+                    ("partner_id", "in", partners.ids),
+                ]
+            )
+        }
+        partners_format = partners.mail_partner_format()
+        for partner in partners:
+            partners_format.get(partner)["persona"] = {
+                "channelMembers": [
+                    (
+                        "insert",
+                        member_by_partner.get(partner)
+                        ._discuss_channel_member_format(
+                            fields={
+                                "id": True,
+                                "channel": {"id"},
+                                "persona": {"partner": {"id"}},
+                            }
+                        )
+                        .get(member_by_partner.get(partner)),
+                    )
+                ],
+            }
+        return list(partners_format.values())
diff --git a/addons/mail/models/discuss/res_users.py b/addons/mail/models/discuss/res_users.py
new file mode 100644
index 00000000000..cbb04975404
--- /dev/null
+++ b/addons/mail/models/discuss/res_users.py
@@ -0,0 +1,49 @@
+# Part of Odoo. See LICENSE file for full copyright and licensing details.
+
+from odoo import api, models
+from odoo.addons.base.models.res_users import is_selection_groups
+
+
+class ResUsers(models.Model):
+    _inherit = "res.users"
+
+    @api.model_create_multi
+    def create(self, vals_list):
+        users = super().create(vals_list)
+        # Auto-subscribe to channels unless skip explicitly requested
+        if not self.env.context.get("discuss_channel_nosubscribe"):
+            self.env["discuss.channel"].search(
+                [("group_ids", "in", users.groups_id.ids)]
+            )._subscribe_users_automatically()
+        return users
+
+    def write(self, vals):
+        res = super().write(vals)
+        if "active" in vals and not vals["active"]:
+            self._unsubscribe_from_non_public_channels()
+        sel_groups = [vals[k] for k in vals if is_selection_groups(k) and vals[k]]
+        if vals.get("groups_id"):
+            # form: {'group_ids': [(3, 10), (3, 3), (4, 10), (4, 3)]} or {'group_ids': [(6, 0, [ids]}
+            user_group_ids = [command[1] for command in vals["groups_id"] if command[0] == 4]
+            user_group_ids += [id for command in vals["groups_id"] if command[0] == 6 for id in command[2]]
+            self.env["discuss.channel"].search([("group_ids", "in", user_group_ids)])._subscribe_users_automatically()
+        elif sel_groups:
+            self.env["discuss.channel"].search([("group_ids", "in", sel_groups)])._subscribe_users_automatically()
+        return res
+
+    def unlink(self):
+        self._unsubscribe_from_non_public_channels()
+        return super().unlink()
+
+    def _unsubscribe_from_non_public_channels(self):
+        """This method un-subscribes users from group restricted channels. Main purpose
+        of this method is to prevent sending internal communication to archived / deleted users.
+        We do not un-subscribes users from public channels because in most common cases,
+        public channels are mailing list (e-mail based) and so users should always receive
+        updates from public channels until they manually un-subscribe themselves.
+        """
+        domain = [("partner_id", "in", self.partner_id.ids)]
+        current_cm = self.env["discuss.channel.member"].sudo().search(domain)
+        current_cm.filtered(
+            lambda cm: (cm.channel_id.channel_type == "channel" and cm.channel_id.group_public_id)
+        ).unlink()
diff --git a/addons/mail/models/ir_attachment.py b/addons/mail/models/ir_attachment.py
index 79145b7d993..ea9a6158c35 100644
--- a/addons/mail/models/ir_attachment.py
+++ b/addons/mail/models/ir_attachment.py
@@ -39,16 +39,15 @@ class IrAttachment(models.Model):
                 related_record.message_main_attachment_id = self
 
     def _delete_and_notify(self):
-        for attachment in self:
-            if attachment.res_model == 'discuss.channel' and attachment.res_id:
-                target = self.env['discuss.channel'].browse(attachment.res_id)
-            else:
-                target = self.env.user.partner_id
-            self.env['bus.bus']._sendone(target, 'ir.attachment/delete', {
-                'id': attachment.id,
-            })
+        self.env['bus.bus']._sendmany((attachment._bus_notification_target(), 'ir.attachment/delete', {
+            'id': attachment.id,
+        }) for attachment in self)
         self.unlink()
 
+    def _bus_notification_target(self):
+        self.ensure_one()
+        return self.env.user.partner_id
+
     def _attachment_format(self, legacy=False):
         safari = request and request.httprequest.user_agent and request.httprequest.user_agent.browser == 'safari'
         res_list = []
diff --git a/addons/mail/models/mail_link_preview.py b/addons/mail/models/mail_link_preview.py
index 438ef226d0f..3dfaca131a1 100644
--- a/addons/mail/models/mail_link_preview.py
+++ b/addons/mail/models/mail_link_preview.py
@@ -42,14 +42,7 @@ class LinkPreview(models.Model):
             link_previews |= self.env['mail.link.preview']._create_link_preview(url, message.id, requests_session)
         if not link_previews:
             return
-        guest = self.env['mail.guest']._get_guest_from_context()
-        if message.model == 'discuss.channel' and message.res_id:
-            target = self.env['discuss.channel'].browse(message.res_id)
-        elif self.env.user._is_public() and guest:
-            target = guest
-        else:
-            target = self.env.user.partner_id
-        self.env['bus.bus']._sendone(target, 'mail.record/insert', {
+        self.env['bus.bus']._sendone(message._bus_notification_target(), 'mail.record/insert', {
             'LinkPreview': link_previews._link_preview_format()
         })
 
@@ -67,13 +60,7 @@ class LinkPreview(models.Model):
         notifications = []
         guest = self.env['mail.guest']._get_guest_from_context()
         for link_preview in self:
-            if link_preview.message_id.model == 'discuss.channel' and link_preview.message_id.res_id:
-                target = self.env['discuss.channel'].browse(link_preview.message_id.res_id)
-            elif self.env.user._is_public() and guest:
-                target = guest
-            else:
-                target = self.env.user.partner_id
-            notifications.append((target, 'mail.link.preview/delete', {
+            notifications.append((link_preview.message_id._bus_notification_target(), 'mail.link.preview/delete', {
                 'id': link_preview.id,
                 'message_id': link_preview.message_id.id,
             }))
diff --git a/addons/mail/models/mail_message.py b/addons/mail/models/mail_message.py
index 507ec888a57..7f1e47b1329 100644
--- a/addons/mail/models/mail_message.py
+++ b/addons/mail/models/mail_message.py
@@ -856,12 +856,10 @@ class Message(models.Model):
     def _message_format(self, fnames, format_reply=True, legacy=False):
         """Reads values from messages and formats them for the web client."""
         vals_list = self._read_format(fnames)
-
         thread_ids_by_model_name = defaultdict(set)
         for message in self:
             if message.model and message.res_id:
                 thread_ids_by_model_name[message.model].add(message.res_id)
-
         for vals in vals_list:
             message_sudo = self.browse(vals['id']).sudo().with_prefetch(self.ids)
             author = {
@@ -890,9 +888,8 @@ class Message(models.Model):
                 'message': {'id': message_sudo.id},
                 'partners': [{'id': partner.id, 'name': partner.name} for partner in reactions.partner_id],
             } for content, reactions in reactions_per_content.items()]
-            if format_reply and message_sudo.model == 'discuss.channel' and message_sudo.parent_id:
-                vals['parentMessage'] = message_sudo.parent_id.message_format(format_reply=False)[0]
             allowed_tracking_ids = message_sudo.tracking_value_ids.filtered(lambda tracking: not tracking.field_groups or self.env.is_superuser() or self.user_has_groups(tracking.field_groups))
+            vals.update(message_sudo._message_format_extras(format_reply))
             vals.update({
                 'author': author,
                 'default_subject': default_subject,
@@ -905,9 +902,12 @@ class Message(models.Model):
                 'pinned_at': message_sudo.pinned_at,
                 'record_name': record_name,
             })
-
         return vals_list
 
+    def _message_format_extras(self, format_reply):
+        self.ensure_one()
+        return {}
+
     @api.model
     def _message_fetch(self, domain, before=None, after=None, around=None, limit=30):
         """ Get a limited amount of formatted messages with provided domain.
@@ -1075,6 +1075,10 @@ class Message(models.Model):
         ]
         self.env['bus.bus']._sendmany(updates)
 
+    def _bus_notification_target(self):
+        self.ensure_one()
+        return self.env.user.partner_id
+
     # ------------------------------------------------------
     # TOOLS
     # ------------------------------------------------------
diff --git a/addons/mail/models/res_groups.py b/addons/mail/models/res_groups.py
deleted file mode 100644
index 4fa3654a72c..00000000000
--- a/addons/mail/models/res_groups.py
+++ /dev/null
@@ -1,23 +0,0 @@
-# -*- coding: utf-8 -*-
-# Part of Odoo. See LICENSE file for full copyright and licensing details.
-
-from odoo import models
-
-
-class ResGroups(models.Model):
-    """ Update of res.groups class
-        - if adding users from a group, check discuss.channels linked to this user
-          group and subscribe them. This is done by overriding the write method.
-    """
-    _name = 'res.groups'
-    _inherit = 'res.groups'
-    _description = 'Access Groups'
-
-    def write(self, vals):
-        res = super(ResGroups, self).write(vals)
-        if vals.get('users'):
-            # form: {'group_ids': [(3, 10), (3, 3), (4, 10), (4, 3)]} or {'group_ids': [(6, 0, [ids]}
-            user_ids = [command[1] for command in vals['users'] if command[0] == 4]
-            user_ids += [id for command in vals['users'] if command[0] == 6 for id in command[2]]
-            self.env['discuss.channel'].search([('group_ids', 'in', self._ids)])._subscribe_users_automatically()
-        return res
diff --git a/addons/mail/models/res_partner.py b/addons/mail/models/res_partner.py
index 5359b0b190e..dc6685d8dff 100644
--- a/addons/mail/models/res_partner.py
+++ b/addons/mail/models/res_partner.py
@@ -20,8 +20,6 @@ class Partner(models.Model):
     parent_id = fields.Many2one(tracking=3)
     user_id = fields.Many2one(tracking=4)
     vat = fields.Char(tracking=5)
-    # channels
-    channel_ids = fields.Many2many('discuss.channel', 'discuss_channel_member', 'partner_id', 'channel_id', string='Channels', copy=False)
     # tracked field used for chatter logging purposes
     # we need this to be readable inline as tracking messages use inline HTML nodes
     contact_address_inline = fields.Char(compute='_compute_contact_address_inline', string='Inlined Complete Address', tracking=True)
@@ -264,71 +262,34 @@ class Partner(models.Model):
         ], limit=100)
         return notifications.mail_message_id._message_notification_format()
 
-    def _get_channels_as_member(self):
-        """Returns the channels of the partner."""
-        self.ensure_one()
-        channels = self.env['discuss.channel']
-        # get the channels and groups
-        channels |= self.env['discuss.channel'].search([
-            ('channel_type', 'in', ('channel', 'group')),
-            ('channel_partner_ids', 'in', [self.id]),
-        ])
-        # get the pinned direct messages
-        channels |= self.env['discuss.channel'].search([
-            ('channel_type', '=', 'chat'),
-            ('channel_member_ids', 'in', self.env['discuss.channel.member'].sudo()._search([
-                ('partner_id', '=', self.id),
-                ('is_pinned', '=', True),
-            ])),
-        ])
-        return channels
+    @api.model
+    def get_mention_suggestions(self, search, limit=8):
+        """ Return 'limit'-first partners' such that the name or email matches a 'search' string.
+            Prioritize partners that are also (internal) users, and then extend the research to all partners.
+            The return format is a list of partner data (as per returned by `mail_partner_format()`).
+        """
+        domain = self._get_mention_suggestions_domain(search)
+        partners = self._search_mention_suggestions(domain, limit)
+        return list(partners.mail_partner_format().values())
 
     @api.model
-    def search_for_channel_invite(self, search_term, channel_id=None, limit=30):
-        """ Returns partners matching search_term that can be invited to a channel.
-        If the channel_id is specified, only partners that can actually be invited to the channel
-        are returned (not already members, and in accordance to the channel configuration).
-        """
-        domain = expression.AND([
+    def _get_mention_suggestions_domain(self, search):
+        return expression.AND([
             expression.OR([
-                [('name', 'ilike', search_term)],
-                [('email', 'ilike', search_term)],
+                [('name', 'ilike', search)],
+                [('email', 'ilike', search)],
             ]),
             [('active', '=', True)],
             [('type', '!=', 'private')],
-            [('user_ids', '!=', False)],
-            [('user_ids.active', '=', True)],
-            [('user_ids.share', '=', False)],
         ])
-        if channel_id:
-            channel = self.env['discuss.channel'].search([('id', '=', int(channel_id))])
-            domain = expression.AND([domain, [('channel_ids', 'not in', channel.id)]])
-            if channel.group_public_id:
-                domain = expression.AND([domain, [('user_ids.groups_id', 'in', channel.group_public_id.id)]])
-        query = self.env['res.partner']._search(domain, order='name, id')
-        query.order = 'LOWER("res_partner"."name"), "res_partner"."id"'  # bypass lack of support for case insensitive order in search()
-        query.limit = int(limit)
-        return {
-            'count': self.env['res.partner'].search_count(domain),
-            'partners': list(self.env['res.partner'].browse(query).mail_partner_format().values()),
-        }
 
     @api.model
-    def get_mention_suggestions(self, search, limit=8, channel_id=None):
-        """ Return 'limit'-first partners' such that the name or email matches a 'search' string.
-            Prioritize partners that are also (internal) users, and then extend the research to all partners.
-            If channel_id is given, only members of this channel are returned.
-            The return format is a list of partner data (as per returned by `mail_partner_format()`).
-        """
-        search_dom = expression.OR([[('name', 'ilike', search)], [('email', 'ilike', search)]])
-        search_dom = expression.AND([[('active', '=', True), ('type', '!=', 'private')], search_dom])
-        if channel_id:
-            search_dom = expression.AND([[('channel_ids', 'in', channel_id)], search_dom])
-        domain_is_user = expression.AND([[('user_ids', '!=', False), ('user_ids.active', '=', True)], search_dom])
+    def _search_mention_suggestions(self, domain, limit):
+        domain_is_user = expression.AND([[('user_ids', '!=', False)], [('user_ids.active', '=', True)], domain])
         priority_conditions = [
             expression.AND([domain_is_user, [('partner_share', '=', False)]]),  # Search partners that are internal users
             domain_is_user,  # Search partners that are users
-            search_dom,  # Search partners that are not users
+            domain,  # Search partners that are not users
         ]
         partners = self.env['res.partner']
         for domain in priority_conditions:
@@ -340,14 +301,7 @@ class Partner(models.Model):
             # really slow.
             query = self._search(expression.AND([[('id', 'not in', partners.ids)], domain]), limit=remaining_limit)
             partners |= self.browse(query)
-        partners_format = partners.mail_partner_format()
-        if channel_id:
-            member_by_partner = {member.partner_id: member for member in self.env['discuss.channel.member'].search([('channel_id', '=', channel_id), ('partner_id', 'in', partners.ids)])}
-            for partner in partners:
-                partners_format.get(partner)['persona'] = {
-                    'channelMembers': [('insert', member_by_partner.get(partner)._discuss_channel_member_format(fields={'id': True, 'channel': {'id'}, 'persona': {'partner': {'id'}}}).get(member_by_partner.get(partner)))],
-                }
-        return list(partners_format.values())
+        return partners
 
     @api.model
     def im_search(self, name, limit=20, excluded_ids=None):
diff --git a/addons/mail/models/res_users.py b/addons/mail/models/res_users.py
index 53320276b50..4f3be5bf0cb 100644
--- a/addons/mail/models/res_users.py
+++ b/addons/mail/models/res_users.py
@@ -2,7 +2,6 @@
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 
 from odoo import _, api, exceptions, fields, models, modules, tools
-from odoo.addons.base.models.res_users import is_selection_groups
 from odoo.tools import email_normalize
 
 
@@ -12,8 +11,6 @@ class Users(models.Model):
         - make a new user follow itself
         - add a welcome message
         - add suggestion preference
-        - if adding groups to a user, check discuss.channels linked to this user
-          group, and the user. This is done by overriding the write method.
     """
     _name = 'res.users'
     _inherit = ['res.users']
@@ -101,9 +98,6 @@ class Users(models.Model):
                         message_type='notification',
                         subtype_xmlid='mail.mt_note'
                     )
-        # Auto-subscribe to channels unless skip explicitly requested
-        if not self.env.context.get('discuss_channel_nosubscribe'):
-            self.env['discuss.channel'].search([('group_ids', 'in', users.groups_id.ids)])._subscribe_users_automatically()
         return users
 
     def write(self, vals):
@@ -159,23 +153,8 @@ class Users(models.Model):
                     mail_values={'email_to': previous_email},
                     suggest_password_reset=False,
                 )
-
-        if 'active' in vals and not vals['active']:
-            self._unsubscribe_from_non_public_channels()
-        sel_groups = [vals[k] for k in vals if is_selection_groups(k) and vals[k]]
-        if vals.get('groups_id'):
-            # form: {'group_ids': [(3, 10), (3, 3), (4, 10), (4, 3)]} or {'group_ids': [(6, 0, [ids]}
-            user_group_ids = [command[1] for command in vals['groups_id'] if command[0] == 4]
-            user_group_ids += [id for command in vals['groups_id'] if command[0] == 6 for id in command[2]]
-            self.env['discuss.channel'].search([('group_ids', 'in', user_group_ids)])._subscribe_users_automatically()
-        elif sel_groups:
-            self.env['discuss.channel'].search([('group_ids', 'in', sel_groups)])._subscribe_users_automatically()
         return write_res
 
-    def unlink(self):
-        self._unsubscribe_from_non_public_channels()
-        return super().unlink()
-
     def _notify_security_setting_update(self, subject, content, mail_values=None, **kwargs):
         """ This method is meant to be called whenever a sensitive update is done on the user's account.
         It will send an email to the concerned user warning him about this change and making some security suggestions.
@@ -239,20 +218,6 @@ class Users(models.Model):
             'update_datetime': fields.Datetime.now(),
         }
 
-    def _unsubscribe_from_non_public_channels(self):
-        """ This method un-subscribes users from group restricted channels. Main purpose
-            of this method is to prevent sending internal communication to archived / deleted users.
-            We do not un-subscribes users from public channels because in most common cases,
-            public channels are mailing list (e-mail based) and so users should always receive
-            updates from public channels until they manually un-subscribe themselves.
-        """
-        current_cm = self.env['discuss.channel.member'].sudo().search([
-            ('partner_id', 'in', self.partner_id.ids),
-        ])
-        current_cm.filtered(
-            lambda cm: (cm.channel_id.channel_type == 'channel' and cm.channel_id.group_public_id)
-        ).unlink()
-
     def _get_portal_access_update_body(self, access_granted):
         body = _('Portal Access Granted') if access_granted else _('Portal Access Revoked')
         if self.partner_id.email:
diff --git a/addons/mail/static/src/composer/suggestion_service.js b/addons/mail/static/src/composer/suggestion_service.js
index 24161b11785..ef01657c10c 100644
--- a/addons/mail/static/src/composer/suggestion_service.js
+++ b/addons/mail/static/src/composer/suggestion_service.js
@@ -37,19 +37,20 @@ export class SuggestionService {
         }
     }
 
+    /**
+     * @param {string} term
+     * @param {import("@mail/core/thread_model").Thread} thread
+     */
     async fetchPartners(term, thread) {
         const kwargs = { search: term };
-        const isNonPublicChannel =
-            thread &&
-            (thread.type === "group" ||
-                thread.type === "chat" ||
-                (thread.type === "channel" && thread.group_based_subscription));
-        if (isNonPublicChannel) {
+        if (thread.model === "discuss.channel") {
             kwargs.channel_id = thread.id;
         }
         const suggestedPartners = await this.orm.call(
             "res.partner",
-            "get_mention_suggestions",
+            thread.model === "discuss.channel"
+                ? "get_mention_suggestions_from_channel"
+                : "get_mention_suggestions",
             [],
             kwargs
         );
diff --git a/addons/mail/static/tests/helpers/mock_server/models/res_partner.js b/addons/mail/static/tests/helpers/mock_server/models/res_partner.js
index a8e215dce37..6ac1959c914 100644
--- a/addons/mail/static/tests/helpers/mock_server/models/res_partner.js
+++ b/addons/mail/static/tests/helpers/mock_server/models/res_partner.js
@@ -20,6 +20,12 @@ patch(MockServer.prototype, "mail/models/res_partner", {
         if (args.model === "res.partner" && args.method === "get_mention_suggestions") {
             return this._mockResPartnerGetMentionSuggestions(args);
         }
+        if (
+            args.model === "res.partner" &&
+            args.method === "get_mention_suggestions_from_channel"
+        ) {
+            return this._mockResPartnerGetMentionSuggestionsFromChannel(args);
+        }
         return this._super(route, args);
     },
 
@@ -30,6 +36,69 @@ patch(MockServer.prototype, "mail/models/res_partner", {
      * @returns {Array[]}
      */
     _mockResPartnerGetMentionSuggestions(args) {
+        const search = (args.args[0] || args.kwargs.search || "").toLowerCase();
+        const limit = args.args[1] || args.kwargs.limit || 8;
+        /**
+         * Returns the given list of partners after filtering it according to
+         * the logic of the Python method `get_mention_suggestions` for the
+         * given search term. The result is truncated to the given limit and
+         * formatted as expected by the original method.
+         *
+         * @param {Object[]} partners
+         * @param {string} search
+         * @param {integer} limit
+         * @returns {Object[]}
+         */
+        const mentionSuggestionsFilter = (partners, search, limit) => {
+            const matchingPartners = [
+                ...this._mockResPartnerMailPartnerFormat(
+                    partners
+                        .filter((partner) => {
+                            // no search term is considered as return all
+                            if (!search) {
+                                return true;
+                            }
+                            // otherwise name or email must match search term
+                            if (partner.name && partner.name.toLowerCase().includes(search)) {
+                                return true;
+                            }
+                            if (partner.email && partner.email.toLowerCase().includes(search)) {
+                                return true;
+                            }
+                            return false;
+                        })
+                        .map((partner) => partner.id)
+                ).values(),
+            ];
+            // reduce results to max limit
+            matchingPartners.length = Math.min(matchingPartners.length, limit);
+            return matchingPartners;
+        };
+
+        // add main suggestions based on users
+        const partnersFromUsers = this.getRecords("res.users", [])
+            .map((user) => this.getRecords("res.partner", [["id", "=", user.partner_id]])[0])
+            .filter((partner) => partner);
+        const mainMatchingPartners = mentionSuggestionsFilter(partnersFromUsers, search, limit);
+
+        let extraMatchingPartners = [];
+        // if not enough results add extra suggestions based on partners
+        const remainingLimit = limit - mainMatchingPartners.length;
+        if (mainMatchingPartners.length < limit) {
+            const partners = this.getRecords("res.partner", [
+                ["id", "not in", mainMatchingPartners.map((partner) => partner.id)],
+            ]);
+            extraMatchingPartners = mentionSuggestionsFilter(partners, search, remainingLimit);
+        }
+        return mainMatchingPartners.concat(extraMatchingPartners);
+    },
+    /**
+     * Simulates `get_channel_mention_suggestions` on `res.partner`.
+     *
+     * @private
+     * @returns {Array[]}
+     */
+    _mockResPartnerGetMentionSuggestionsFromChannel(args) {
         const search = (args.args[0] || args.kwargs.search || "").toLowerCase();
         const limit = args.args[1] || args.kwargs.limit || 8;
         const channel_id = args.args[2] || args.kwargs.channel_id;
@@ -50,14 +119,12 @@ patch(MockServer.prototype, "mail/models/res_partner", {
                 ...this._mockResPartnerMailPartnerFormat(
                     partners
                         .filter((partner) => {
-                            if (channel_id) {
-                                const [member] = this.getRecords("discuss.channel.member", [
-                                    ["channel_id", "=", channel_id],
-                                    ["partner_id", "=", partner.id],
-                                ]);
-                                if (!member) {
-                                    return false;
-                                }
+                            const [member] = this.getRecords("discuss.channel.member", [
+                                ["channel_id", "=", channel_id],
+                                ["partner_id", "=", partner.id],
+                            ]);
+                            if (!member) {
+                                return false;
                             }
                             // no search term is considered as return all
                             if (!search) {
@@ -75,22 +142,20 @@ patch(MockServer.prototype, "mail/models/res_partner", {
                         .map((partner) => partner.id)
                 ).values(),
             ].map((partnerFormat) => {
-                if (channel_id) {
-                    const [member] = this.getRecords("discuss.channel.member", [
-                        ["channel_id", "=", channel_id],
-                        ["partner_id", "=", partnerFormat.id],
-                    ]);
-                    partnerFormat["persona"] = {
-                        channelMembers: [
-                            [
-                                "insert",
-                                this._mockDiscussChannelMember_DiscussChannelMemberFormat([
-                                    member.id,
-                                ]),
-                            ],
+                const [member] = this.getRecords("discuss.channel.member", [
+                    ["channel_id", "=", channel_id],
+                    ["partner_id", "=", partnerFormat.id],
+                ]);
+                partnerFormat["persona"] = {
+                    channelMembers: [
+                        [
+                            "insert",
+                            this._mockDiscussChannelMember_DiscussChannelMemberFormat([
+                                member.id,
+                            ])[0],
                         ],
-                    };
-                }
+                    ],
+                };
                 return partnerFormat;
             });
             // reduce results to max limit
diff --git a/addons/mail/tests/test_discuss_channel.py b/addons/mail/tests/test_discuss_channel.py
index 67313f6d2ff..0211fa2d761 100644
--- a/addons/mail/tests/test_discuss_channel.py
+++ b/addons/mail/tests/test_discuss_channel.py
@@ -6,7 +6,7 @@ from datetime import datetime
 from unittest.mock import patch
 
 from odoo import Command, fields
-from odoo.addons.mail.models.discuss_channel import channel_avatar, group_avatar
+from odoo.addons.mail.models.discuss.discuss_channel import channel_avatar, group_avatar
 from odoo.addons.mail.tests.common import mail_new_test_user
 from odoo.addons.mail.tests.common import MailCommon
 from odoo.exceptions import AccessError, UserError