diff --git a/api/etemplate.php b/api/etemplate.php
index 14a3f31310..31ac42ff3b 100644
--- a/api/etemplate.php
+++ b/api/etemplate.php
@@ -420,22 +420,24 @@ function send_template()
 			return "<et2-date$matches[1] $matches[2]></et2-date$matches[1]>";
 		}, $str);
 
-		// replace <tree(-cat)? multiple="..." with <et2-tree(-cat)(-multiple) and fix attributes
+		// replace <tree(-cat)? multiple="..." with <et2-tree(-cat) and fix attributes
 		$str = preg_replace_callback('#<tree(-cat)?\s(.*?)\s*/>#s', static function (array $matches)
 		{
 			$tag = 'et2-tree'.($matches[1] ?? '');
 			$attrs = parseAttrs($matches[2]);
-			if (!empty($attrs['multiple']) && $attrs['multiple'] !== 'false' ||
-			   !empty($attrs['options']) && (int)$attrs['options'] > 1)
+			if (!empty($attrs['options']) && (int)$attrs['options'] > 1)
 			{
-				$tag .= '-multiple';
+				$attrs['multiple'] = 'true';
 			}
 			// fix renamed attrs, thought regular under_score to camelCase happens later
 			if (!empty($attrs['parent_node'])) $attrs['parentId'] = $attrs['parent_node'];
-			unset($attrs['multiple'], $attrs['options'], $attrs['parent_node']);
+			unset($attrs['options'], $attrs['parent_node']);
 			return "<$tag" . stringAttrs($attrs) . "></$tag>";
 		}, $str);
 
+		// replace no longer used <et2-tree-multiple.../> with <et2-tree multiple="true".../>
+		$str = preg_replace('#<et2-tree-multiple ([^>]+)(/>|</et2-tree-multiple>)#', '<et2-tree multiple="true" $1></et2-tree>', $str);
+
 		if ($template === 'mobile')
 		{
 		}
diff --git a/mail/templates/default/folder_management.xet b/mail/templates/default/folder_management.xet
index bc465a0e79..f2a308674d 100644
--- a/mail/templates/default/folder_management.xet
+++ b/mail/templates/default/folder_management.xet
@@ -6,7 +6,9 @@
 			<et2-description  value="Folder Management" class="mail_folder_management_header"></et2-description>
 		</et2-hbox>
 		<et2-hbox  class="treeContainer">
-			<et2-tree-multiple id="tree" multiple="true" autoloading="mail_ui::ajax_folderMgmtTree_autoloading" multimarking="strict" oncheck="app.mail.folderMgmt_onCheck" onselect="app.mail.folderMgmt_onSelect" onopenstart="app.mail.folderMgmt_autoloadingStart" onopenend="app.mail.folderMgmt_autoloadingEnd" highlighting="true"/>
+			<et2-tree id="tree" multiple="true" autoloading="mail_ui::ajax_folderMgmtTree_autoloading" multimarking="strict"
+				oncheck="app.mail.folderMgmt_onCheck" onselect="app.mail.folderMgmt_onSelect" onopenstart="app.mail.folderMgmt_autoloadingStart"
+				onopenend="app.mail.folderMgmt_autoloadingEnd" highlighting="true"></et2-tree>
 		</et2-hbox>
 		<et2-hbox  class="dialogFooterToolbar">
 			<et2-button  statustext="Delete" label="Delete" id="button[delete]" onclick="app.mail.folderMgmt_deleteBtn"></et2-button>
diff --git a/mail/templates/default/subscribe.xet b/mail/templates/default/subscribe.xet
index e9b43760a4..943e7ee9ff 100755
--- a/mail/templates/default/subscribe.xet
+++ b/mail/templates/default/subscribe.xet
@@ -6,7 +6,10 @@
 			<et2-description  value="Subscription folders" class="mail_subscription_header"></et2-description>
 		</et2-hbox>
 		<et2-hbox  class="treeContainer">
-			<et2-tree-multiple id="foldertree" multiple="true" autoloading="mail_ui::ajax_tree_autoloading" onopenstart="app.mail.subscription_autoloadingStart" onopenend="app.mail.subscription_autoloadingEnd" multimarking="strict" highlighting="true" oncheck="app.mail.folderMgmt_onCheck" onselect="app.mail.folderMgmt_onSelect"/>
+			<et2-tree id="foldertree" multiple="true" autoloading="mail_ui::ajax_tree_autoloading"
+				onopenstart="app.mail.subscription_autoloadingStart" onopenend="app.mail.subscription_autoloadingEnd"
+				multimarking="strict" highlighting="true" oncheck="app.mail.folderMgmt_onCheck"
+				onselect="app.mail.folderMgmt_onSelect"></et2-tree>
 		</et2-hbox>
 		<et2-hbox  class="dialogFooterToolbar">
 			<et2-button  statustext="Saves subscription changes" label="Save" id="button[save]"></et2-button>