On Tue, Sep 4, 2012 at 6:07 AM, Ibrahim <ibrahim1@gmail.com> wrote:
I've read old archive about blocking SMTP port (TCP port 25). In my current situation we are mobile operator and use NAT for our subscribers and we have few spammers, a bit difficult to track it because mostly our subscribers are prepaid services. If we block TCP port 25, there might be "good" subscribers will not be able to send email.
Hi, There are no "good" subscribers trying to send email direct to a remote port 25 from behind a NAT. The "good" subscribers are either using your local smart host or they're using TCP port 587 on their remote mail server. You may safely block outbound TCP with a destination of port 25 from behind your NAT without harming reasonable use of your network.
We are thinking to block MX queries on our DNS server, so only spammer that use their own SMTP server will got affected. All DNS queries from our subscribers already redirected to our DNS cache servers. But seem Bind don't have feature to block MX query. Any best practice to block MX query?
Best practice is: don't mess with the DNS. I don't know if any resolver software supports what you want to do here. If it does, I don't know what the repercussions are likely to be. I do know that historically, altering DNS results has proven problematic. For example, returning an A record for your search server in place of no-host responses wreaks all manner of havoc. I also doubt the efficacy of the method. Were this to become common practice, a spammer could trivially evade it by using his own DNS software or simply pumping out the address list along with pre-resolved IP addresses to deliver the mail to. For all I know, they already do. Regards, Bill Herrin -- William D. Herrin ................ herrin@dirtside.com bill@herrin.us 3005 Crane Dr. ...................... Web: <http://bill.herrin.us/> Falls Church, VA 22042-3004