[Exim] Not send mail to sender?

I set up mail list this way:

list:       user1@???, user2@???, user3@???

How can I tell exim not to send mail back to a user on the list who
wrote to the list?

Stef
-- 
WebMaster D-WERK
President SOS-ETH 
ETH Zurich
stef@???        http://hoes.li