diff --git a/addons/mass_mailing/static/src/scss/mailing_filter_widget.scss b/addons/mass_mailing/static/src/scss/mailing_filter_widget.scss
index a0c4476ff67..c95e3fc9936 100644
--- a/addons/mass_mailing/static/src/scss/mailing_filter_widget.scss
+++ b/addons/mass_mailing/static/src/scss/mailing_filter_widget.scss
@@ -1,4 +1,5 @@
-.o_form_view .o_mass_mailing_filter_container {
+.o_form_view .o_mass_mailing_filter_container,
+.o_legacy_form_view .o_mass_mailing_filter_container {
     .o_mass_mailing_add_filter, .o_mass_mailing_remove_filter {
         cursor: pointer;
     }
diff --git a/addons/mass_mailing/static/src/scss/mass_mailing.scss b/addons/mass_mailing/static/src/scss/mass_mailing.scss
index 120482af250..1b0de618a99 100644
--- a/addons/mass_mailing/static/src/scss/mass_mailing.scss
+++ b/addons/mass_mailing/static/src/scss/mass_mailing.scss
@@ -1,4 +1,5 @@
-.o_form_view.o_mass_mailing_mailing_form {
+.o_form_view .o_mass_mailing_mailing_form,
+.o_legacy_form_view.o_mass_mailing_mailing_form {
 
     input.o_field_char.o_field_widget {
         padding-right: 40px; // Avoid overlapping subject text on emoji widget
@@ -14,14 +15,16 @@
 }
 
 @include media-breakpoint-up(lg, $o-extra-grid-breakpoints) {
-    .o_form_view .o_form_sheet .o_notebook .tab-content .tab-pane .o_mail_body {
+    .o_form_view .o_form_sheet .o_notebook .tab-content .tab-pane .o_mail_body,
+    .o_legacy_form_view .o_form_sheet .o_notebook .tab-content .tab-pane .o_mail_body {
         // cancel the padding of the form_sheet when breakpoints are reached
         margin-left: -$o-sheet-cancel-hpadding*2;
         margin-right: -$o-sheet-cancel-hpadding*2;
     }
 }
 
-.o_form_view.o_mass_mailing_mailing_form.o_mass_mailing_form_full_width {
+.o_form_view .o_mass_mailing_mailing_form.o_mass_mailing_form_full_width,
+.o_legacy_form_view.o_mass_mailing_mailing_form.o_mass_mailing_form_full_width {
     .o_form_statusbar {
         margin-bottom: 0;
 
@@ -54,7 +57,8 @@
     }
 }
 
-.o_form_view.o_mass_mailing_mailing_form {
+.o_form_view .o_mass_mailing_mailing_form,
+.o_legacy_form_view.o_mass_mailing_mailing_form {
     .o_mass_mailing_subject {
         // Place the favorite button without breaking the emoji widget
         padding-right: 50px;
@@ -162,7 +166,8 @@
     }
 }
 
-.o_form_view .o_group.o_inner_group.o_mass_mailing_mailing_group {
+.o_form_view .o_group.o_inner_group.o_mass_mailing_mailing_group,
+.o_legacy_form_view .o_group.o_inner_group.o_mass_mailing_mailing_group {
     // Used to gain extra space in form.
     display: block;
 }
@@ -187,12 +192,14 @@
     }
 }
 
-.o_form_view.o_xxl_form_view.o_mass_mailing_mailing_form {
+.o_form_view.o_xxl_form_view .o_mass_mailing_mailing_form,
+.o_legacy_form_view.o_xxl_form_view.o_mass_mailing_mailing_form {
     // This will hide the chatter scroll bar
     height: initial;
 }
 
-.o_form_view {
+.o_form_view,
+.o_legacy_form_view {
     // This will display the emoji widget in the right position after a text field with sms option.
     .o_sms_container ~ .o_mail_add_emoji{
         bottom: 55px;
diff --git a/addons/mass_mailing/static/src/scss/mass_mailing.ui.scss b/addons/mass_mailing/static/src/scss/mass_mailing.ui.scss
index c67f47e21f7..01f7e66c63e 100644
--- a/addons/mass_mailing/static/src/scss/mass_mailing.ui.scss
+++ b/addons/mass_mailing/static/src/scss/mass_mailing.ui.scss
@@ -1,4 +1,5 @@
-.o_form_view .o_form_sheet .o_notebook .tab-content .tab-pane .o_mail_body {
+.o_form_view .o_form_sheet .o_notebook .tab-content .tab-pane .o_mail_body,
+.o_legacy_form_view .o_form_sheet .o_notebook .tab-content .tab-pane .o_mail_body {
     // cancel padding of form_sheet
     margin-top: -$o-sheet-cancel-tpadding;
     margin-left: -$o-sheet-cancel-hpadding;
diff --git a/addons/mass_mailing/views/mailing_mailing_views.xml b/addons/mass_mailing/views/mailing_mailing_views.xml
index 93c4a7dc47b..81150e73b3f 100644
--- a/addons/mass_mailing/views/mailing_mailing_views.xml
+++ b/addons/mass_mailing/views/mailing_mailing_views.xml
@@ -277,8 +277,8 @@
                                         <label for="ab_testing_enabled"/>
                                         <span class="d-flex">
                                             <field name="ab_testing_enabled" attrs="{'readonly': [('state', '!=', 'draft')]}" force_save="1"/>
-                                            <span class="col" attrs="{'invisible': [('ab_testing_enabled', '=', False)]}">
-                                                on <field name="ab_testing_pc" class="col-6 text-center"
+                                            <span class="d-flex" attrs="{'invisible': [('ab_testing_enabled', '=', False)]}">
+                                                on <field name="ab_testing_pc" class="mx-1 text-center"
                                                     attrs="{'readonly': [('state', '!=', 'draft')]}"/> %
                                             </span>
                                         </span>
@@ -453,6 +453,9 @@
                 <xpath expr="//notebook/page[@name='chat']" position="inside">
                     <xpath expr="//div[hasclass('oe_chatter')]" position="move"/>
                 </xpath>
+                <xpath expr="//div[hasclass('oe_chatter')]" position="attributes">
+                    <attribute name="class" remove="o-aside"/>
+                </xpath>
                 <xpath expr="//notebook/page[@name='mail_body']" position="after">
                     <page string="Mail Debug" name="mail_debug" groups="base.group_no_one">
                         <div class="position-relative">