diff --git a/addons/web_editor/static/src/js/common/utils.js b/addons/web_editor/static/src/js/common/utils.js
index c96c832fcc5..16fa0e08db0 100644
--- a/addons/web_editor/static/src/js/common/utils.js
+++ b/addons/web_editor/static/src/js/common/utils.js
@@ -87,6 +87,7 @@ const DEFAULT_PALETTE = {
 const BACKGROUND_IMAGE_ATTRIBUTES = new Set([
     "originalId", "originalSrc", "mimetype", "resizeWidth", "glFilter", "quality", "bgSrc",
     "filterOptions",
+    "mimetypeBeforeConversion",
 ]);
 
 /**
diff --git a/addons/web_editor/static/src/js/editor/image_processing.js b/addons/web_editor/static/src/js/editor/image_processing.js
index 2c688b62ca3..0aa452236f4 100644
--- a/addons/web_editor/static/src/js/editor/image_processing.js
+++ b/addons/web_editor/static/src/js/editor/image_processing.js
@@ -443,7 +443,9 @@ export async function activateCropper(image, aspectRatio, dataset) {
 export async function loadImageInfo(img, rpc, attachmentSrc = '') {
     const src = attachmentSrc || img.getAttribute('src');
     // If there is a marked originalSrc, the data is already loaded.
-    if (img.dataset.originalSrc || !src) {
+    // If the image does not have the "mimetypeBeforeConversion" attribute, it
+    // has to be added.
+    if ((img.dataset.originalSrc && img.dataset.mimetypeBeforeConversion) || !src) {
         return;
     }
 
@@ -465,9 +467,14 @@ export async function loadImageInfo(img, rpc, attachmentSrc = '') {
     // The "redirect" check is for when it is a redirect image attachment due to
     // an external URL upload.
     if (original && original.image_src && !/\/web\/image\/\d+-redirect\//.test(original.image_src)) {
+        if (!img.dataset.mimetype) {
+            // The mimetype has to be added only if it is not already present as
+            // we want to avoid to reset a mimetype set by the user.
+            img.dataset.mimetype = original.mimetype;
+        }
         img.dataset.originalId = original.id;
         img.dataset.originalSrc = original.image_src;
-        img.dataset.mimetype = original.mimetype;
+        img.dataset.mimetypeBeforeConversion = original.mimetype;
     }
 }
 
diff --git a/addons/web_editor/static/src/js/editor/snippets.options.js b/addons/web_editor/static/src/js/editor/snippets.options.js
index e5f301861e3..0b85cea88ca 100644
--- a/addons/web_editor/static/src/js/editor/snippets.options.js
+++ b/addons/web_editor/static/src/js/editor/snippets.options.js
@@ -5780,9 +5780,9 @@ const ImageHandlerOption = SnippetOptionWidget.extend({
         };
         widths[img.naturalWidth] = [_t("%spx", img.naturalWidth), 'image/webp'];
         widths[optimizedWidth] = [_t("%spx (Suggested)", optimizedWidth), 'image/webp'];
-        const imgMimetype = this._getImageMimetype(img);
-        widths[maxWidth] = [_t("%spx (Original)", maxWidth), imgMimetype];
-        if (imgMimetype !== 'image/webp') {
+        const mimetypeBeforeConversion = img.dataset.mimetypeBeforeConversion;
+        widths[maxWidth] = [_t("%spx (Original)", maxWidth), mimetypeBeforeConversion];
+        if (mimetypeBeforeConversion !== "image/webp") {
             // Avoid a key collision by subtracting 0.1 - putting the webp
             // above the original format one of the same size.
             widths[maxWidth - 0.1] = [_t("%spx", maxWidth), 'image/webp'];
diff --git a/odoo/tools/mail.py b/odoo/tools/mail.py
index 1c9881306ae..b9a9e6f48ae 100644
--- a/odoo/tools/mail.py
+++ b/odoo/tools/mail.py
@@ -37,6 +37,7 @@ safe_attrs = clean.defs.safe_attrs | frozenset(
      'data-class', 'data-mimetype', 'data-original-src', 'data-original-id', 'data-gl-filter', 'data-quality', 'data-resize-width',
      'data-shape', 'data-shape-colors', 'data-file-name', 'data-original-mimetype',
      'data-behavior-props', 'data-prop-name',  # knowledge commands
+     'data-mimetype-before-conversion',
      ])
 SANITIZE_TAGS = {
     # allow new semantic HTML5 tags