diff --git a/addons/mass_mailing/static/src/js/mailing_mailing_view_form_full_width.js b/addons/mass_mailing/static/src/js/mailing_mailing_view_form_full_width.js
index f4a58a5e230..67c370c8e1a 100644
--- a/addons/mass_mailing/static/src/js/mailing_mailing_view_form_full_width.js
+++ b/addons/mass_mailing/static/src/js/mailing_mailing_view_form_full_width.js
@@ -105,12 +105,10 @@ export class MassMailingFullWidthViewController extends formView.Controller {
      */
     _onToggleFullscreen() {
         const $iframeDoc = this.$iframe.contents();
-        const iframeTarget = $iframeDoc.find('#iframe_target');
+        const html = $iframeDoc.find('html').get(0);
+        html.scrollTop = 0;
+        html.classList.toggle('o_fullscreen');
         const isFullscreen = this._isFullScreen();
-        iframeTarget.css({
-            display: isFullscreen ? '' : 'flex',
-            'flex-direction': isFullscreen ? '' : 'column',
-        });
         const wysiwyg = $iframeDoc.find('.note-editable').data('wysiwyg');
         if (wysiwyg && wysiwyg.snippetsMenu) {
             // Restore the appropriate scrollable depending on the mode.
@@ -118,6 +116,7 @@ export class MassMailingFullWidthViewController extends formView.Controller {
             wysiwyg.snippetsMenu.$scrollable = isFullscreen ? $iframeDoc.find('.note-editable') : this._$scrollable;
         }
         this._repositionMailingEditorSidebar();
+        this._resizeMailingEditorIframe();
     }
     /**
      * Return true if the mailing editor is in full screen mode, false
@@ -138,19 +137,18 @@ export class MassMailingFullWidthViewController extends formView.Controller {
      * @private
      */
     _resizeMailingEditorIframe() {
-        const VERTICAL_OFFSET = 12; // Vertical offset picked for visual design purposes.
-        const minHeight = $(window).height() - Math.abs(this.$iframe.offset().top) - (VERTICAL_OFFSET / 2);
+        const minHeight = $(window).height() - Math.abs(this.$iframe.offset().top);
         const $iframeDoc = this.$iframe.contents();
         const $themeSelectorNew = $iframeDoc.find('.o_mail_theme_selector_new');
         if ($themeSelectorNew.length) {
-            this.$iframe.height(Math.max($themeSelectorNew[0].scrollHeight + VERTICAL_OFFSET, minHeight));
+            this.$iframe.height(Math.max($themeSelectorNew[0].scrollHeight, minHeight));
         } else {
             const ref = $iframeDoc.find('#iframe_target')[0];
             if (ref) {
                 this.$iframe.css({
                     height: this._isFullScreen()
                         ? $(window).height()
-                        : Math.max(ref.scrollHeight + VERTICAL_OFFSET, minHeight),
+                        : Math.max(ref.scrollHeight, minHeight),
                 });
             }
         }
diff --git a/addons/mass_mailing/static/src/js/mass_mailing_html_field.js b/addons/mass_mailing/static/src/js/mass_mailing_html_field.js
index 644134c0478..1e2b15db610 100644
--- a/addons/mass_mailing/static/src/js/mass_mailing_html_field.js
+++ b/addons/mass_mailing/static/src/js/mass_mailing_html_field.js
@@ -562,6 +562,7 @@ MassMailingHtmlField.props = {
     ...HtmlField.props,
     filterTemplates: { type: Boolean, optional: true },
     inlineField: { type: String, optional: true },
+    iframeHtmlClass: { type: String, optional: true },
 };
 
 MassMailingHtmlField.displayName = _lt("Email");
@@ -572,6 +573,7 @@ MassMailingHtmlField.extractProps = (...args) => {
         ...htmlProps,
         filterTemplates: attrs.options.filterTemplates,
         inlineField: attrs.options['inline-field'],
+        iframeHtmlClass: attrs['iframeHtmlClass'],
     };
 };
 
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 ed24a947887..a15b62057ba 100644
--- a/addons/mass_mailing/static/src/scss/mass_mailing.ui.scss
+++ b/addons/mass_mailing/static/src/scss/mass_mailing.ui.scss
@@ -7,10 +7,15 @@
     margin-bottom: -$o-sheet-cancel-bpadding;
 }
 
-html, body {
+html:not(.o_mass_mailing_iframe), body:not(.o_mass_mailing_iframe), html.o_fullscreen {
     overflow: visible !important;
 }
 
+#iframe_target:not(.o_fullscreen) {
+    display: flex;
+    flex-direction: column;
+}
+
 .o_mail_theme_selector {
     > a {
         height: $o-we-toolbar-height;
diff --git a/addons/mass_mailing/views/mailing_mailing_views.xml b/addons/mass_mailing/views/mailing_mailing_views.xml
index 1dd4948176d..a1af5512eee 100644
--- a/addons/mass_mailing/views/mailing_mailing_views.xml
+++ b/addons/mass_mailing/views/mailing_mailing_views.xml
@@ -443,6 +443,9 @@
                 <xpath expr="//div[hasclass('oe_chatter')]" position="attributes">
                     <attribute name="class" remove="o-aside"/>
                 </xpath>
+                <xpath expr="//notebook/page[@name='mail_body']//field[@name='body_arch']" position="attributes">
+                    <attribute name="iframeHtmlClass">o_mass_mailing_iframe</attribute>
+                </xpath>
                 <xpath expr="//notebook/page[@name='mail_body']" position="after">
                     <!-- test_01_mass_mailing_editor_tour -->
                     <field name="body_html" invisible="1"/>
diff --git a/addons/web_editor/static/src/js/backend/html_field.js b/addons/web_editor/static/src/js/backend/html_field.js
index aef093a398c..a8f76e08830 100644
--- a/addons/web_editor/static/src/js/backend/html_field.js
+++ b/addons/web_editor/static/src/js/backend/html_field.js
@@ -603,6 +603,7 @@ HtmlField.extractProps = ({ attrs, field }) => {
             noAttachment: attrs.options['no-attachment'],
             inIframe: Boolean(attrs.options.cssEdit),
             iframeCssAssets: attrs.options.cssEdit,
+            iframeHtmlClass: attrs.iframeHtmlClass,
             snippets: attrs.options.snippets,
             allowCommandVideo: Boolean(attrs.options.allowCommandVideo) && (!field.sanitize || !field.sanitize_tags),
             mediaModalParams: {
diff --git a/addons/web_editor/static/src/js/wysiwyg/wysiwyg_iframe.js b/addons/web_editor/static/src/js/wysiwyg/wysiwyg_iframe.js
index 1ab602e205f..8d2b5454aad 100644
--- a/addons/web_editor/static/src/js/wysiwyg/wysiwyg_iframe.js
+++ b/addons/web_editor/static/src/js/wysiwyg/wysiwyg_iframe.js
@@ -149,7 +149,9 @@ Wysiwyg.include({
                 });
                 self.$iframe[0].contentWindow.document
                     .open("text/html", "replace")
-                    .write(`<!DOCTYPE html><html>${iframeContent}</html>`);
+                    .write(`<!DOCTYPE html><html${
+                        self.options.iframeHtmlClass ? ` class="${self.options.iframeHtmlClass}"` : ''
+                    }>${iframeContent}</html>`);
             });
             self.options.document = self.$iframe[0].contentWindow.document;
         });