Now I want to allow LAN users to send emails to each other on LAN but want to allow some LAN users to send email to Internet(Outside world). Is there any way using Linux iptables firewall to acieve this requirement.
I will assume that LAN users are allowed to connect to mail server only, and not to outside world. Controlling this on Sendmail level would be much more simpler and efficient. Assuming you are using Sendmail as your MTA. Netfilter isn't suited for this, because there's no way for it to know if SMTP connection between client (LAN user) and server is delivery of email addressed to another LAN user, or to somebody at the outside. Also, Sendmail will take care of generating appropriate error messages back to the users, while Netfilter would simply block the traffic without any explanation to the user what happened.
-- Aleksandar Milivojevic <amilivojevic@xxxxxx> Pollard Banknote Limited Systems Administrator 1499 Buffalo Place Tel: (204) 474-2323 ext 276 Winnipeg, MB R3T 1L7
