diff --git a/mail/js/app.js b/mail/js/app.js
index 27e147c60e..465d3de44d 100644
--- a/mail/js/app.js
+++ b/mail/js/app.js
@@ -40,7 +40,7 @@ app.classes.mail = AppJS.extend(
 		timeout: null,
 		request: null
 	},
-	
+
 	/**
 	 * abbrevations for common access rights
 	 * @array
@@ -2456,4 +2456,26 @@ app.classes.mail = AppJS.extend(
 		}
 	},
 
+	/**
+	 * Lock tree so it does NOT receive any more mouse-clicks
+	 */
+	lock_tree: function()
+	{
+		if (!document.getElementById('mail_folder_lock_div'))
+		{
+			var parent = jQuery('#mail-index_nm\\[foldertree\\]');
+			var lock_div = jQuery(document.createElement('div'));
+			lock_div.attr('id', 'mail_folder_lock_div')
+				.addClass('mail_folder_lock');
+			parent.prepend(lock_div);
+		}
+	},
+
+	/**
+	 * Unlock tree so it receives again mouse-clicks after calling lock_tree()
+	 */
+	unlock_tree: function()
+	{
+		jQuery('#mail_folder_lock_div').remove();
+	}
 });
diff --git a/mail/templates/default/app.css b/mail/templates/default/app.css
index 5d68da3728..599d5a0a58 100644
--- a/mail/templates/default/app.css
+++ b/mail/templates/default/app.css
@@ -567,3 +567,23 @@ div.mailPreviewHeaders #mail-index_previewAttachmentArea.visible {
 .mail_extraEmails.visible > a {
 	display: list-item;
 }
+
+/**
+ * Lock div for tree to prevent further clicks
+ */
+#mail-index_nm\[foldertree\] {
+	position: relative;
+}
+#mail_folder_lock_div {
+	position: absolute;
+	left: 0;
+	top: 0;
+	width: 100%;
+	height: 100%;
+	z-index: 10000;
+	// only change styling below:
+	background-image: url(../../../phpgwapi/templates/default/images/ajax-loader.gif);
+	background-position: left top;
+	background-repeat: no-repeat;
+	background-color: rgba(255,255,255,0.5);
+}