diff --git a/lib/Providers/Mail/Service.php b/lib/Providers/Mail/Service.php
index 2bbb900..028f8c5 100644
--- a/lib/Providers/Mail/Service.php
+++ b/lib/Providers/Mail/Service.php
@@ -484,17 +484,34 @@ class Service implements ServiceBaseInterface, ServiceMutableInterface, ServiceC
             }
         }
 
-        // we need to determine if the folder being deleted is already in the trash
-        if (str_starts_with((string) $target->collection(), (string) $deleteTargetIdentifier?->collection())) {
-            // if so, we should hard delete instead of moving to avoid duplicates in the trash
-            $deleteMode = 'hard';
+        if ($deleteMode === 'soft') {
+            $targetMailbox = $this->mailService->collectionFetch((string) $target->collection());
+            if ($targetMailbox === null) {
+                throw new \RuntimeException('Collection not found for delete operation');
+            }
+
+            $targetIdentifier = (string) $target->collection();
+            $trashIdentifier = (string) $deleteTargetIdentifier->collection();
+            $parentIdentifier = isset($targetMailbox['parentId'])
+                ? (string) $targetMailbox['parentId']
+                : null;
+
+            // JMAP mailbox IDs are opaque, so containment must be determined
+            // from parentId rather than by comparing ID prefixes.
+            if ($targetIdentifier === $trashIdentifier || $parentIdentifier === $trashIdentifier) {
+                $deleteMode = 'hard';
+            }
         }
 
-        $result = match ($deleteMode) {
-            'soft' => $this->collectionMove($deleteTargetIdentifier, $target),
-            'hard' => $this->mailService->collectionDestroy($target->collection(), $force),
-        };
-        return $result;
+        if ($deleteMode === 'soft') {
+            return $this->collectionMove($deleteTargetIdentifier, $target);
+        }
+
+        if ($this->mailService->collectionDestroy((string) $target->collection(), $force) === null) {
+            throw new \RuntimeException("Failed to delete collection: {$target->collection()}");
+        }
+
+        return true;
     }
 
     public function collectionMove(CollectionIdentifier $target, CollectionIdentifier $source): CollectionBaseInterface