Internal e-mail Reccomendations?
 

Hello to all,

One of the items Office XP no longer offers or supports is Microsoft Mail, meaning we would have to send all our internal e-mails out through internet e-mail accounts, which we are loathe to do. I also need a good Linux project to get my feet wet, and would like reccomendations on an application that would provide interoffice e-mail, and if it offers a way for us to post e-mail messages as threads for general brainstorming sessions and group input, That would be even better.
We currently have 30 workstations and one server, plus additional surplus desktops and a spare server to experiment with for this project.
Any suggestions?