Always show default mailbox in all MailboxView, Search Mailbox and Settings

model/lib/extensions/list_presentation_mailbox_extension.dart

@@ -6,6 +6,9 @@ extension ListPresentationMailboxExtension on List<PresentationMailbox> {
   List<PresentationMailbox> get listSubscribedMailboxes =>
     where((mailbox) => mailbox.isSubscribedMailbox).toList();
 
+  List<PresentationMailbox> get listSubscribedMailboxesAndDefaultMailboxes =>
+    where((mailbox) => mailbox.isSubscribedMailbox || mailbox.isDefault).toList();
+
   List<PresentationMailbox> get listPersonalMailboxes =>
     where((mailbox) => mailbox.isPersonal).toList();
 }

model/lib/mailbox/presentation_mailbox.dart

@@ -105,6 +105,8 @@ class PresentationMailbox with EquatableMixin {
     (namespace?.value.indexOf('[') ?? 0) + 1,
     namespace?.value.indexOf(']'));
 
+  bool get allowedToDisplay => isSubscribedMailbox || isDefault;
+
   @override
   List<Object?> get props => [
     id,