Blocking MX query

[Ibrahim <ibrahim1 () gmail com>]

Hi All,

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.
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?


Regards
Ibrahim