diff --git a/addons/mail/models/mail_activity.py b/addons/mail/models/mail_activity.py
index 921e06f7d47..19ca810f1fe 100644
--- a/addons/mail/models/mail_activity.py
+++ b/addons/mail/models/mail_activity.py
@@ -113,9 +113,10 @@ class MailActivity(models.Model):
 
         for record in self.filtered(lambda activity: activity.date_deadline):
             today = today_default
-            if record.user_id.tz:
+            tz = record.user_id.sudo().tz
+            if tz:
                 today_utc = pytz.UTC.localize(datetime.utcnow())
-                today_tz = today_utc.astimezone(pytz.timezone(record.user_id.tz))
+                today_tz = today_utc.astimezone(pytz.timezone(tz))
                 today = date(year=today_tz.year, month=today_tz.month, day=today_tz.day)
 
             date_deadline = fields.Date.from_string(record.date_deadline)