diff --git a/mail_activity_done/models/mail_activity.py b/mail_activity_done/models/mail_activity.py
index 5730f40e79..bfb10cee1c 100644
--- a/mail_activity_done/models/mail_activity.py
+++ b/mail_activity_done/models/mail_activity.py
@@ -1,5 +1,9 @@
 # Copyright 2018-22 ForgeFlow <http://www.forgeflow.com>
 # License LGPL-3.0 or later (http://www.gnu.org/licenses/lgpl.html).
+from datetime import datetime
+
+import pytz
+
 from odoo import api, fields, models
 from odoo.osv import expression
 
@@ -92,3 +96,77 @@ def _read_progress_bar(self, domain, group_by, progress_bar):
         """
         domain = expression.AND([domain, [("activity_ids.done", "=", False)]])
         return super()._read_progress_bar(domain, group_by, progress_bar)
+
+    def _search_activity_state(self, operator, value):
+        # Totally override the method.
+        all_states = {"overdue", "today", "planned", False}
+        if operator == "=":
+            search_states = {value}
+        elif operator == "!=":
+            search_states = all_states - {value}
+        elif operator == "in":
+            search_states = set(value)
+        elif operator == "not in":
+            search_states = all_states - set(value)
+
+        reverse_search = False
+        if False in search_states:
+            # If we search "activity_state = False", they might be a lot of records
+            # (million for some models), so instead of returning the list of IDs
+            # [(id, 'in', ids)] we will reverse the domain and return something like
+            # [(id, 'not in', ids)], so the list of ids is as small as possible
+            reverse_search = True
+            search_states = all_states - search_states
+
+        # Use number in the SQL query for performance purpose
+        integer_state_value = {
+            "overdue": -1,
+            "today": 0,
+            "planned": 1,
+            False: None,
+        }
+
+        search_states_int = {integer_state_value.get(s or False) for s in search_states}
+
+        query = """
+          SELECT res_id
+            FROM (
+                SELECT res_id,
+                       -- Global activity state
+                       MIN(
+                            -- Compute the state of each individual activities
+                            -- -1: overdue
+                            --  0: today
+                            --  1: planned
+                           SIGN(EXTRACT(day from (
+                                mail_activity.date_deadline - DATE_TRUNC(
+                                'day', %(today_utc)s AT TIME ZONE res_partner.tz)
+                           )))
+                        )::INT AS activity_state
+                  FROM mail_activity
+             LEFT JOIN res_users
+                    ON res_users.id = mail_activity.user_id
+             LEFT JOIN res_partner
+                    ON res_partner.id = res_users.partner_id
+                 WHERE mail_activity.res_model = %(res_model_table)s
+                 and mail_activity.done=False
+              GROUP BY res_id
+            ) AS res_record
+          WHERE %(search_states_int)s @> ARRAY[activity_state]
+        """
+
+        self._cr.execute(
+            query,
+            {
+                "today_utc": pytz.utc.localize(datetime.utcnow()),
+                "res_model_table": self._name,
+                "search_states_int": list(search_states_int),
+            },
+        )
+        return [
+            (
+                "id",
+                "not in" if reverse_search else "in",
+                [r[0] for r in self._cr.fetchall()],
+            )
+        ]
diff --git a/mail_activity_done/tests/test_mail_activity_done.py b/mail_activity_done/tests/test_mail_activity_done.py
index f481de3ec8..2c78758b15 100644
--- a/mail_activity_done/tests/test_mail_activity_done.py
+++ b/mail_activity_done/tests/test_mail_activity_done.py
@@ -14,6 +14,7 @@ def setUp(self):
                 "company_id": self.env.ref("base.main_company").id,
                 "name": "Test User",
                 "login": "testuser",
+                "tz": "Europe/Brussels",
                 "groups_id": [(6, 0, [self.env.ref("base.group_user").id])],
             }
         )
@@ -56,3 +57,14 @@ def test_read_progress_bar(self):
         self.assertEqual(self.act1.state, "done")
         result = res_partner._read_progress_bar(**params)
         self.assertEqual(len(result), 0)
+
+    def test_activity_state_search(self):
+        today_activities = self.env["res.partner"].search(
+            [("activity_state", "=", "today")]
+        )
+        self.assertEqual(len(today_activities), 1)
+        self.act1._action_done()
+        today_activities = self.env["res.partner"].search(
+            [("activity_state", "=", "today")]
+        )
+        self.assertEqual(len(today_activities), 0)