[Exim] blocking reply to alias?

I have a silly goal (in that I know there are probably better ways to do
it).

That said, I am using a simple alias to send mail to a small list of
users. My concern is that I do not want anyone else to be able to send
mail to this alias.

I like the idea that the mail received looks like it is from me, to
"mylist@???" - thereby hiding the actual recipients. However,
I am concerned that someone might learn of this address (one of the
recipients even) and use it to send unauthorized mail to my
correspondents.

Can exim prevent anyone but myself from sending to this address in a
simple way, or do I need to install some sort of mailing list
program? (I hope not, for something this simple) Or is there a better
way to send the mail (from a script) and preserve the anonymity of
the other recipients?

aloha,
dave