I need to create a mailing-list for members of my organization to use to reach everyone at once. I want them to be able to just send mail to something like firstname.lastname@example.org and have it forward to everybody's email. By the way, all of the email addresses are under a different domain. They do not use my server to check or send mail.
I've toyed with some different software but haven't been able to get anything to work yet. What do you guys think I should use?