diff --git a/addons/mail/models/mail_activity.py b/addons/mail/models/mail_activity.py
index 47b724aac98..02507b46928 100644
--- a/addons/mail/models/mail_activity.py
+++ b/addons/mail/models/mail_activity.py
@@ -6,6 +6,7 @@ import pytz
 
 from odoo import api, exceptions, fields, models, _
 from odoo.osv import expression
+from odoo.tools import pycompat
 
 
 class MailActivityType(models.Model):
@@ -34,6 +35,10 @@ class MailActivityType(models.Model):
         'Planned in', default=0,
         help='Number of days before executing the action. It allows to plan the action deadline.')
     icon = fields.Char('Icon', help="Font awesome icon e.g. fa-tasks")
+    decoration_type = fields.Selection([
+        ('warning', 'Alert'),
+        ('danger', 'Error')], string="Decoration Type",
+        help="Change the background color of the related activities of this type.")
     res_model_id = fields.Many2one(
         'ir.model', 'Model', index=True,
         domain=['&', ('is_mail_thread', '=', True), ('transient', '=', False)],
@@ -85,6 +90,7 @@ class MailActivity(models.Model):
         'mail.activity.type', 'Activity',
         domain="['|', ('res_model_id', '=', False), ('res_model_id', '=', res_model_id)]", ondelete='restrict')
     activity_category = fields.Selection(related='activity_type_id.category')
+    activity_decoration = fields.Selection(related='activity_type_id.decoration_type')
     icon = fields.Char('Icon', related='activity_type_id.icon')
     summary = fields.Char('Summary')
     note = fields.Html('Note')
diff --git a/addons/mail/static/src/js/activity.js b/addons/mail/static/src/js/activity.js
index 828e29e195d..9c86104603f 100644
--- a/addons/mail/static/src/js/activity.js
+++ b/addons/mail/static/src/js/activity.js
@@ -201,8 +201,12 @@ var Activity = AbstractActivityField.extend({
      */
     _render: function () {
         _.each(this._activities, function (activity) {
-            if (activity.note) {
+            var note = mailUtils.parseAndTransform(activity.note || '', mailUtils.inline);
+            var is_blank = (/^\s*$/).test(note);
+            if (!is_blank) {
                 activity.note = mailUtils.parseAndTransform(activity.note, mailUtils.addLink);
+            } else {
+                activity.note = '';
             }
         });
         var activities = setDelayLabel(this._activities);
diff --git a/addons/mail/static/src/scss/mail_activity.scss b/addons/mail/static/src/scss/mail_activity.scss
index f835275e873..d4d9a3ffecb 100644
--- a/addons/mail/static/src/scss/mail_activity.scss
+++ b/addons/mail/static/src/scss/mail_activity.scss
@@ -89,6 +89,10 @@
 
             .o_thread_message_note {
                 margin: 2px 0 5px;
+                padding: 0px;
+            }
+            .o_thread_message_warning {
+                margin: 2px 0 5px;
             }
 
             .o_thread_message_tools {
diff --git a/addons/mail/static/src/xml/activity.xml b/addons/mail/static/src/xml/activity.xml
index 5ed86b37614..1e9892b4d1e 100644
--- a/addons/mail/static/src/xml/activity.xml
+++ b/addons/mail/static/src/xml/activity.xml
@@ -51,7 +51,7 @@
                                 </dl>
                             </div>
                         </div>
-                        <div t-if="activity.note" class="o_thread_message_note small">
+                        <div t-if="activity.note" t-attf-class="o_thread_message_#{activity.activity_decoration} #{activity.activity_decoration ? 'alert alert-' + activity.activity_decoration : ''} small">
                             <t t-raw="activity.note"/>
                         </div>
                         <div class="o_thread_message_tools btn-group">
diff --git a/addons/mail/views/mail_activity_views.xml b/addons/mail/views/mail_activity_views.xml
index 56908319829..343de996f81 100644
--- a/addons/mail/views/mail_activity_views.xml
+++ b/addons/mail/views/mail_activity_views.xml
@@ -21,6 +21,7 @@
                             <field name="res_model_id" groups="base.group_no_one"/>
                             <field name="summary"/>
                             <field name="icon" groups="base.group_no_one"/>
+                            <field name="decoration_type" groups="base.group_no_one"/>
                             <label for="days"/>
                             <div>
                                 <field name="days" class="oe_inline"/>