static int mailbox_is_virtannot(struct mailbox *mailbox, const char *entry)
{
    if (mailbox->i.minor_version < 13) return 0;
    // thrid was introduced in v13
    if (!strcmp(entry, IMAP_ANNOT_NS "thrid")) return 1;

    if (mailbox->i.minor_version < 15) return 0;
    // savedate was introduced in v15
    if (!strcmp(entry, IMAP_ANNOT_NS "savedate")) return 1;

    if (mailbox->i.minor_version < 16) return 0;
    // createdmodseq was introduced in v16
    if (!strcmp(entry, IMAP_ANNOT_NS "createdmodseq")) return 1;

    return 0;
}
static int mailbox_is_virtannot(struct mailbox *mailbox, const char *entry)
{
    if (mailbox->i.minor_version < 13) return 0;
     
    if (!strcmp(entry, IMAP_ANNOT_NS "thrid")) return 1;

    if (mailbox->i.minor_version < 15) return 0;
     
    if (!strcmp(entry, IMAP_ANNOT_NS "savedate")) return 1;

    if (mailbox->i.minor_version < 16) return 0;
     
    if (!strcmp(entry, IMAP_ANNOT_NS "createdmodseq")) return 1;

    return 0;
}