hmm..
when I make a new list of people
that forms a chat group,
I give it a name
and then just type that name in the to: field,
but I guess this doesn't help you
since the emails of the others are probably shown anyway.
maybe what you are asking is impossible unless you make a group wich works in the way that one send to one (bot) email, and all the others get the email with only the from: field containing personal info.
I dunno really...