Auto-reply to ticket
I think WHMCS Should have a bulit in or Addon open to the public that auto-repliesto ticket.
WHMCS currently has this feature for their site but it was as developed for use with whmcs.com specifically and isn't publicly available. It will be a great feature for the public to use becuase it will let clients know that their ticket is being processed or it can give important infomation to a client without them signing on to their emails.
I have attached a image of WHMC's Auto-reply to ticket.