Out-of-office response to tickets for staff absent

How can I setup as a user so if he/she is out-of-office and a client sends said person an email to an existing ticket that they are assigned with, the sender will see a reply from them advising of their absence..so then they will at least know it may not be responded on immediately.

To add to this, how would a user, say with admin as I, be able to look at all existing tickets and visibly see which ones require further response, i.e. client has replied to tickets, now showing in bold which can normally only be seen by the owner of the ticket.

For a Customer Support tool there must be a greater level of transparency, clients must be able to see their ticket owner are not in-office and someone should be able to, in others staff's absence, be able to view all tickets held by all staff and identify which ones are in bold, thus have responses awaiting - and act on their behalf.

Makes perfect Customer Support sense....