user can turn on/off the including sender in header option

app/dashboard/views/setting.py

@@ -315,6 +315,15 @@ def setting():
                 return redirect(url_for("dashboard.setting"))
             Session.commit()
             flash("Your preference has been updated", "success")
+        elif request.form.get("form-name") == "sender-header":
+            choose = request.form.get("enable")
+            if choose == "on":
+                current_user.include_header_email_header = True
+            else:
+                current_user.include_header_email_header = False
+            Session.commit()
+            flash("Your preference has been updated", "success")
+            return redirect(url_for("dashboard.setting"))
         elif request.form.get("form-name") == "export-data":
             return redirect(url_for("api.export_data"))
         elif request.form.get("form-name") == "export-alias":

templates/dashboard/setting.html

@@ -520,6 +520,30 @@
       </div>
     </div>
 
+    <div class="card" id="sender-header">
+      <div class="card-body">
+        <div class="card-title">Include original sender in email headers
+        </div>
+        <div class="mb-3">
+          SimpleLogin forwards emails to your mailbox from the <b>reverse-alias</b> and not from the <b>original</b> sender address. <br>
+          If this option is enabled, the original sender addresses is stored in the email header <b>X-SimpleLogin-Envelope-From</b>.
+          You can choose to display this header in your email client. <br>
+          As email headers aren't encrypted, your mailbox service can know the sender address via this header.
+        </div>
+        <form method="post" action="#sender-header">
+          <input type="hidden" name="form-name" value="sender-header">
+
+          <div class="form-check">
+            <input type="checkbox" id="include-sender-header" name="enable"
+                {% if current_user.include_header_email_header %} checked {% endif %} class="form-check-input">
+            <label for="include-sender-header">Include sender address in email headers</label>
+          </div>
+
+          <button type="submit" class="btn btn-outline-primary">Update</button>
+        </form>
+      </div>
+    </div>
+
     <div class="card">
       <div class="card-body">
         <div class="card-title">Alias Import</div>