how can i restrict internal user to send and receive email from other/outside domain?

how can i restrict internal user to send and receive email from other/outside domain? The only emails that he can only get is internal mail. We're having pop3 server on machine1 and smtp on machine2.
mlgatchalianAsked:
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ksematCommented:
Sending is easy. You can simply make sendmail masquerade all mail form your smtp server to appear as user@your.domain.com edit /etc/sendmail.cf and change this line to:

# Who I masquerade as ( null for no masquerading)
DMyour.domain.com

now all mail sent through this server will appear to come from his username@you.domain.com even when he explicitly sets another domain in his mailer.

But you then have to restrict his internet access so that he cannot use public services like yahoo and hotmail otherwise he is through. Which may not be practical.
However you can block him using ipchains rules such that he cannot connect to ports 25 and 110 of any other servers other than yours in the firewall.


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mlgatchalianAuthor Commented:
linux sendmail issue
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ksematCommented:
Actually a better way to block the users os to do an ipchains redirect such that all connections to port 110 anywhere are redirected to your local pop servers 110 and all connections to port 25 are also redirected to port 25 on your local smtp server.
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samriCommented:
i think by blocking outgoing SMTP, POP, and maybe IMAP on your firewall (if you have any) and only allow incoming/outgoing for your SMTP servers, will deny your local users while allowing your SMTP/POP server to still operate.  (just like ksemat suggestion).

Next step is to ADVERTISE it to your users.

I would say that port redirection will confuse your user even more.  Just tell them that they can't access POP/SMTP to external servers.

good luck.
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samriCommented:
any luck on this?
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