I don't know if this would be useful for a lot of people but it would be useful for me.

Basically what would be great is to have some sort of internal note except it's just another email function.
Something the ticket owner cannot see, maybe because they shouldn't, or it won't make sense.

We currently have 2 needs for this, the first being because our staff are not IT savvy they often get really confused when I CC in somebody to the ticket to ask a technical question - 9 times out of 10 I get a reply from the ticket owner saying "I don't know"
The other use would be for emailing someones manager and you don't want the ticket owner to see the email - often this is just for getting approval to do something but it would still be very useful.