Need alias for announce list?

I get this error when I send to an announce list. The list contains only addresses (each in daily use), and I’m sending from the Dreamhost webmail interface.

I believe I need to set up an alias to point to the announce list, which I’ve tried, but I can’t find the right settings. Thanks for any suggestions. host[] said: 550 Recipient address rejected: User unknown in virtual
alias table (in reply to RCPT TO command)