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Originally Posted by ask2me007  My server is under NAT router.Actually the mail server is behind NAT and only port 25,7071 is forwarded to NAT. |
Then you don't necessarily need a firewall in this situation.
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Originally Posted by ask2me007 As you said some machines in my NAT is sending spams.How can i stop these kind of activities??? |
In that case you must take an inventory of what machines are on your LAN and which ones are sending spam and how they're doing it. If you have machines sending spam then you will continue to get blacklisted, this is an internal security problem.