diff --git a/addons/mail/static/src/widgets/form_renderer/form_renderer.scss b/addons/mail/static/src/widgets/form_renderer/form_renderer.scss
index e509a5ac574..405608e1cb5 100644
--- a/addons/mail/static/src/widgets/form_renderer/form_renderer.scss
+++ b/addons/mail/static/src/widgets/form_renderer/form_renderer.scss
@@ -37,11 +37,11 @@
         border-top: 1px solid $border-color;
     }
 
-    &:not(.o-aside) .o_ChatterContainer {
-            @include make-container-max-widths();
+    &:not(.o-aside):not(.o-full-width) .o_ChatterContainer {
+        @include make-container-max-widths();
 
-            margin-left: auto;
-            margin-right: auto;
+        margin-left: auto;
+        margin-right: auto;
     }
 }
 
diff --git a/addons/mass_mailing/views/mailing_mailing_views.xml b/addons/mass_mailing/views/mailing_mailing_views.xml
index 1a43b40e0a7..e089c75eb03 100644
--- a/addons/mass_mailing/views/mailing_mailing_views.xml
+++ b/addons/mass_mailing/views/mailing_mailing_views.xml
@@ -442,7 +442,7 @@
                     <xpath expr="//div[hasclass('oe_chatter')]" position="move"/>
                 </xpath>
                 <xpath expr="//div[hasclass('oe_chatter')]" position="attributes">
-                    <attribute name="class" remove="o-aside"/>
+                    <attribute name="class" remove="o-aside" add="o-full-width" separator=" "/>
                 </xpath>
                 <xpath expr="//notebook/page[@name='mail_body']//field[@name='body_arch']" position="attributes">
                     <attribute name="iframeHtmlClass">o_mass_mailing_iframe</attribute>