Linux mail gateway - help!
I'm a linux newbie trying to set up a linux mail gateway. I have a small office, around 50 people. Currently our email is hosted by a commercial provider and each of the 50 email clients in the office connects directly to the provider to send / receive email. What I would like to do is set up a mail gateway that downloads and distributes email from this provider (I guess I can use fetchmail or getmail for this) but I also would like something which will deliver emails within the LAN without the need of going to the internet when clients are in the office, but when sending email out to someone else outside I want the local mail gateway to send it to the providers smtp server rather than direct delivery. So I need a mail gateway setup rather than a full blown mail server. ie. I want everything to go through the provider. Can anyone help me with this? Thanks.