Index: sope-mime/NGImap4/NGImap4Folder.m
--- sope-mime/NGImap4/NGImap4Folder.m.orig
+++ sope-mime/NGImap4/NGImap4Folder.m
@@ -300,7 +300,7 @@ static int FetchNewUnseenMessagesInSubFoldersOnDemand 
   msn  = [[dict objectForKey:@"search"] mutableCopy];
   
   if ((msn == nil) || ![msn isNotEmpty]) {
-    mes = [NSArray array];
+    mes = [NSMutableArray array];
   }
   else {
     NSEnumerator *seq = nil;
