Restricting posting to Mailing List

Here is what I am trying to do and am hoping that someone has an idea of 
how.

I have a mailing list, I do not want subscribers to be able to post to 
it. I want to be able to send an email to the list that will go out to 
the whole list without having the extra step of having to approve it as 
the moderator.

Basically along the lines of broadcast email.

Thanks for any help.

Cheryl Jorgensen
Update Management