diff --git a/addons/web_editor/static/src/js/wysiwyg/widgets/dialog.js b/addons/web_editor/static/src/js/wysiwyg/widgets/dialog.js
index b46e43ab051..48828b68e0c 100644
--- a/addons/web_editor/static/src/js/wysiwyg/widgets/dialog.js
+++ b/addons/web_editor/static/src/js/wysiwyg/widgets/dialog.js
@@ -1,6 +1,7 @@
 odoo.define('wysiwyg.widgets.Dialog', function (require) {
 'use strict';
 
+var config = require('web.config');
 var core = require('web.core');
 var Dialog = require('web.Dialog');
 
@@ -15,6 +16,9 @@ var SummernoteDialog = Dialog.extend({
      */
     init: function (parent, options) {
         this.options = options || {};
+        if (config.device.isMobile) {
+            options.fullscreen = true;
+        }
         this._super(parent, _.extend({}, {
             buttons: [{
                     text: this.options.save_text || _t("Save"),
@@ -36,10 +40,19 @@ var SummernoteDialog = Dialog.extend({
             self.$el.closest('.modal').on('hidden.bs.modal', self.options.onClose);
         });
         this.on('closed', this, function () {
+            self._toggleFullScreen();
             this.trigger(this.destroyAction, this.final_data || null);
         });
     },
-
+    /**
+     * Only use on config.device.isMobile, it's used by mass mailing to allow the dialog opening on fullscreen
+     * @private
+     */
+    _toggleFullScreen: function() {
+        if (config.device.isMobile && !this.hasFullScreen) {
+            $('#iframe_target[isMobile="true"] #web_editor-top-edit .o_fullscreen').click();
+        }
+    },
     //--------------------------------------------------------------------------
     // Public
     //--------------------------------------------------------------------------
@@ -52,6 +65,15 @@ var SummernoteDialog = Dialog.extend({
         this.destroyAction = "save";
         this.close();
     },
+    /**
+     * @override
+     * @returns {*}
+     */
+    open: function() {
+        this.hasFullScreen = $(window.top.document.body).hasClass('o_field_widgetTextHtml_fullscreen');
+        this._toggleFullScreen();
+        return this._super.apply(this, arguments);
+    },
 });
 
 return SummernoteDialog;
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 c0709a2c90e..6757797c82c 100644
--- a/addons/web_editor/static/src/js/wysiwyg/wysiwyg_iframe.js
+++ b/addons/web_editor/static/src/js/wysiwyg/wysiwyg_iframe.js
@@ -4,6 +4,7 @@ odoo.define('web_editor.wysiwyg.iframe', function (require) {
 var Wysiwyg = require('web_editor.wysiwyg');
 var ajax = require('web.ajax');
 var core = require('web.core');
+var config = require('web.config');
 
 var qweb = core.qweb;
 var promiseCommon;
@@ -87,6 +88,7 @@ Wysiwyg.include({
                 }
                 delete window.top[self._onUpdateIframeId];
                 var $iframeTarget = self.$iframe.contents().find('#iframe_target');
+                $iframeTarget.attr("isMobile", config.device.isMobile);
                 $iframeTarget.find('.o_editable').html(self.$target.val());
                 self.options.toolbarHandler = $('#web_editor-top-edit', self.$iframe[0].contentWindow.document);
                 $(qweb.render('web_editor.FieldTextHtml.fullscreen'))
diff --git a/addons/web_editor/static/src/scss/web_editor.common.scss b/addons/web_editor/static/src/scss/web_editor.common.scss
index 43f174e2862..d4ad43d6a89 100644
--- a/addons/web_editor/static/src/scss/web_editor.common.scss
+++ b/addons/web_editor/static/src/scss/web_editor.common.scss
@@ -401,3 +401,94 @@ a.o_underline {
         @extend %o-nocontent-empty-document;
     }
 }
+
+@include media-breakpoint-down(sm) {
+    // modal select media
+    .o_technical_modal {
+        // see template 'web_editor.FieldTextHtml.fullscreen'
+        z-index: 2001;
+
+        > .o_select_media_dialog {
+            max-width: inherit !important;
+            z-index: 2001;
+
+            .modal-dialog, .model-content {
+                height: 100%;
+            }
+
+            .modal-body {
+                .nav .nav-item.search {
+                    width: 100%;
+
+                    .btn-group {
+                        display: flex;
+                        justify-content: space-around;
+                        padding: 5px;
+                    }
+                }
+
+                // center pictogram
+                .font-icons-icons {
+                    text-align: center;
+                }
+
+                // fix search image
+                .form-control.o_we_search {
+                    height: inherit;
+                }
+
+                .form-inline {
+                    .btn-group {
+                        width: 100%;
+
+                        .btn.btn-primary:not(.dropdown-toggle) {
+                            width: 90%;
+                        }
+                    }
+
+                    > .input-group.ml-2 {
+                        margin-left: 0 !important;
+
+                        > .input-group-append {
+                            width: 100%;
+
+                            > .btn {
+                                width: 100%;
+                            }
+
+                            > .ml-2 {
+                                margin-left: 0 !important;
+                            }
+                        }
+                    }
+                }
+
+                // attachment cells
+                .o_we_existing_attachments > .row {
+                    flex-direction: column;
+
+                    > .o_existing_attachment_cell {
+                        flex: initial;
+                        max-width: 100%;
+
+                        > .o_existing_attachment_remove {
+                            opacity: inherit;
+                            top: 10px;
+                        }
+                    }
+                }
+
+                // select media dialog unsplash error
+                #editor-media-image .unsplash_img_container .unsplash_error .mx-auto {
+                    width: 100%;
+
+                    .form-group {
+                        input.w-100 {
+                            min-width: 100px;
+                        }
+                    }
+                }
+            }
+        }
+    }
+}